Compositions and methods for overcoming resistance to tramadol

ABSTRACT

There is disclosed a composition for oral administration of O-desmethyltramadol. Compositions are also provided that are effective for overcoming resistance to tramadol in patients.

CROSS-REFERENCE TO RELATED APPLICATION

The present patent application claims priority to U.S. provisionalpatent application No. 61/506,092 filed 9 Jul. 2011 the entire contentsof which are incorporated herein by reference.

GOVERNMENT RIGHTS

The invention was made with government support under Grant NumberDA027304 awarded by the National Institutes of Health. The governmenthas certain rights in this invention.

BACKGROUND Technical Field

This disclosure provides pharmaceutical compositions comprisingO-desmethyltramadol for oral administration.

U.S. Pat. No. 3,652,589 discloses a genus of phenol ethers, which aredescribed as having analgesic properties. The genus includes (1R,2R or1S,2S)-2-((dimethylamino)methyl)-1-(3-methoxyphenyl)-cyclohexanol),which has been given the generic name “tramadol.” Tramadol (marketed asthe HCl salt) is a synthetic atypical, centrally-acting opioid analgesicused for treating moderate to severe pain with efficacy and potencyranging between weak opioids and highly potent opioids such as morphine(Raffa et al., “Opioid and nonopioid components independently contributeto the mechanism of action of tramadol, an ‘atypical’ opioid analgesic”J. Pharmacol. Exp. Ther., 1992. 260(1): p. 275-85).

Tramadol was developed by the German pharmaceutical company GrunenthalGmbH in the late 1970s under the trade name TRAMAL®. One of theadvantages of tramadol over traditional opioids is its lower risk ofopioid dependence, resulting in it having an unscheduled status in theU.S. and other countries. (Raffa, “Basic pharmacology relevant to drugabuse assessment: tramadol as example” J. Clin. Pharm. Ther., 2008.33(2): p. 101-8).

Tramadol is a racemate consisting of 1R,2R-tramadol [(+)-tramadol], and1S,2S-tramadol [(−)-tramadol]. After oral administration of theracemate, both the (−) and (+) forms of both tramadol and the M1metabolite (i.e., both the 1R,2R-isomer and 1S,2S-isomer ofO-desmethyltramadol) are detected in the circulation.

At least two synergistic mechanisms appear operative in providinganalgesic activity: binding to μ-opioid receptors and inhibition ofreuptake of norepinephrine and serotonin. (Raffa et al., “Opioid andnonopioid components independently contribute to the mechanism of actionof tramadol, an ‘atypical’ opioid analgesic” J. Pharmacol. Exp. Ther.,1992. 260(1): p. 275-85). The monoaminergic activity of the parent makesa significant contribution to analgesia by blocking nociceptive impulsesat the spinal level.

Consistent with non-opioid mechanisms of analgesia, tramadol inducedanalgesia is only partially antagonized by the opiate antagonistnaloxone in animals and humans (Raffa et al., “Opioid and nonopioidcomponents independently contribute to the mechanism of actionoftramadol, an ‘atypical’ opioid analgesic” J. Pharmacol. Exp. Ther.,1992. 260(1): p. 275-85; Kayser et al., “Effects of the analgesicagenttramadol in normal and arthritic rats: comparison with the effectsof different opioids, including tolerance and cross-tolerance tomorphine “Eur. J. Pharmacol., 1991. 195(1): p. 37-45; Kayser et al.,“Evidence for a noradrenergic component in the antinociceptive effect ofthe analgesic agent tramadol in an animal model of clinical pain, thearthritic rat” Eur. J. Pharmacol., 1992. 224(1): p. 83-8; Collart etal., “Partial inhibition of tramadol antinociceptive effect by naloxonein man” Br. J. Clin. Pharmacol., 1993. 35: p. 73P). Likewise, in adouble-blind, placebo-controlled, crossover study in volunteers,tramadol analgesia was reduced by more than half by an adrenergicreceptor antagonist, consistent with tramadol's non-opioid analgesicmechanism involving inhibition of neuronal uptake of norepinephrine(Desmeules et al., “Contribution of monoaminergic modulation to theanalgesic effect of tramadol” Br. J. Clin. Pharmacol., 1996. 41(1): p.7-12).

This dual and synergistic mechanism of action is further attributed tocomplementary and interactive, mechanisms of action of each tramadolenantiomer. The (+)-enantiomer of tramadol exhibits a 10-fold higheranalgesic activity due to a greater affinity for the p-receptor and is amore effective inhibitor of serotonin reuptake, while the (−)-enantiomeris a more effective inhibitor of noradrenalin reuptake and increasesnoradrenaline release by auto receptor activation. (Raffa et al.,“Complementary and synergistic antinociceptive interaction between theenantiomers of tramadol” J. Pharmacol. Exp. Ther., 1993. 267(1): p.331-40).

In addition to treating pain, tramadol and 0-desmethyltramadol are saidto be effective for treating premature ejaculation (U.S. Pat. No.6,974,839) and urinary incontinence (U.S. Pat. No. 6,660,774), and eachas their single (−) enantiomer are said to be effective for theprevention or treatment of nausea and vomiting (U.S. Pat. No.6,297,286). Tramadol itself is said to be effective for treating coughs,inflammatory and allergic reactions, depression, obsessive-compulsivespectrum disorders, drug and/or alcohol abuse, gastritis, diarrhea,cardiovascular disease, respiratory disease, mental illness and/orepilepsy (U.S. Pat. Nos. 6,387,956 and 6,723,343 and Rojas-Corrales etal., “Tramadol Induces Antidepressant-Type Effects In Mice” LifeSciences, 1998. vol. 63, No. 12).

Resistance to Tramadol Analgesia

Tramadol is rapidly and extensively metabolized in the liver. Theprincipal metabolic pathways involve cytochrome P-450 isoenzymes 2D6 and2B6 (O-desmethylation) and 3A4 (N-desmethylation). Importantly,production of both enantiomers of M1 (i.e., 1R,2R—O-desmethyltramadol or‘(+)-M1’, and 1S,2S—O-desmethyltramadol or ‘(−)-M1’) is dependent on thepolymorphic isoenzyme of the debrisoquine-type, cytochrome P450 2D6(CYP2D6). Approximately 10% of Caucasians have a genotype resulting inreduced activity of CYP2D6. These individuals are poor metabolizers (PM)of tramadol, and they exhibit resistance to tramadol analgesia anddiminished or absent M1 in their blood (Kirchheiner et al., “Effects ofthe CYP2D6 gene duplication on the pharmacokinetics and pharmacodynamicsof tramadol” J. Clin. Psychopharmacol., 2008. 28(1): p. 78-83).

Several human clinical studies have shown that tramadol efficacy issignificantly decreased or lacking in PM patients. In the first study,using two parallel, randomized, double-blind, placebo-controlledcrossover designs, the analgesic effect of tramadol was assessed in 27volunteers (fifteen extensive metabolizers ‘Ems’ and twelve PMs) usingseveral experimental pain models (Poulsen et al., “The hypoalgesiceffect of tramadol in relation to CYP2D6” Clin. Pharmacol. Ther., 1996.60(6): p. 636-44). Differences existed between EMs and PMs thatindicated M1 was critical for a portion of the analgesic effect oftramadol.

In the second study, the effect of CYP450-2D6 polymorphism on tramadolanalgesia was assessed in 300 Caucasian patients undergoing majorabdominal surgery (Stamer et al., “Impact of CYP2D6 genotype onpostoperative tramadol analgesia” Pain, 2003. 105(1-2): p. 231-8).Patients who had one or more functional alleles were classified as EMs.Genotyping revealed that 35 patients were PMs. Compared to the EMs, thePMs displayed a significantly higher incidence of non-response (P=0.005)and required more tramadol or rescue medication (P=0.02).

In the third study, the effect of CYP450-2D6 polymorphism (specificallyCYP450-2D6*10, a SNP (single nucleotide polymorphism) that results in aPro34 to Ser substitution and reduced CYP450-2D6 metabolic activity) ontramadol-induced analgesia (administered via PCA) was assessed in 63Chinese patients who underwent gastrectomy for gastric cancer (Wang etal., “Effect of the CYP2D6* 10 C188T polymorphism on postoperativetramadol analgesia in a Chinese population” Eur. J. Clin. Pharmacol.,2006. 62(11): p. 927-31). The patients were classified as EMs (N=17) oreither heterozygous (N=26) or homozygous (n=20) for CYP2D6*10. Comparedto the other groups, the homozygous group required more tramadol(P<0.05).

Finally, a fourth study of patients (N=187) undergoing major abdominalsurgery reported a 4-fold greater non-response rate to tramadol inCYP450-2D6 poor metabolizers (Stamer et al., “Concentrations of tramadoland 0-desmethyltramadol enantiomers in different CYP2D6 genotypes” Clin.Pharmacol. Ther., 2007. 82(1): p. 41-7). In summary, for mild tomoderate pain, both opioid and non-opioid components oftramadolcontribute to analgesia. The analgesic effect of tramadol is decreasedor absent in patients who have low CYP450-2D6 enzymatic activity(CYP450-2D6, ‘poor metabolizers’ or PMs) because their M1 serumconcentration is considerably less than that in other genotypes.

Sensitivity to the Adverse Events of Tramadol

Approximately 2% of northern white European, and 7% of southernEuropeans carry the CYP2D6 gene duplication (more than two functionalalleles) that results in ultra-rapid metabolism of tramadol, and theseultra-rapid metabolizers (UMs) are more sensitive to the adverse eventsof tramadol than other genotypes (Kirchheiner et al., “Effects of theCYP2D6 gene duplication on the pharmacokinetics and pharmacodynamics oftramadol” J. Clin. Psychopharmacol., 2008. 28(1): p. 78-83). Inparticular, the pharmacokinetics and effects were monitored after asingle dose of 100 mg racemic tramadol in 11 UMs and 11 EMs (i.e., twoactive alleles). Almost 50% of the UM group experienced nausea comparedwith only 9% of the EM group.

M1 Metabolite (O-desmethyltramadol)

Potschka et al. dosed female Wistar rats (intraperitoneal) with the(+)-M1 enantiomer followed by observation for adverse effects (Potschkaet al., “Anticonvulsant and proconvulsant effects of tramadol, itsenantiomers and its M1 metabolite in the rat kindling model of epilepsy”Br. J. Pharmacol., 2000. 131(2): p. 203-12). Garrido et al. dosed maleSprague-Dawley rats i.v. (intravenous) with the (+)-M1 enantiomer alone,or (+)-M1 together with the (−)-M1 enantiomer (Garrido et al., “Modelingof the in vivo antinociceptive interaction between an opioid agonist,(+)-O-desmethyltramadol, and a monoamine reuptake inhibitor,(−)-O-desmethyltramadol, in rats” J. Pharmacol. Exp. Ther., 2000.295(1): p. 352-9). KuKanich and Papich administered i.v. racemic M1 tobeagle dogs (KuKanich and Papich, “Pharmacokinetics of tramadol and themetabolite O-desmethyltramadol in dogs” J. Vet. Pharmacol. Ther., 2004.27(4): p. 239-46).

SUMMARY

This disclosure provides a pharmaceutical composition comprising the M1metabolite of tramadol (i.e., O-desmethyltramadol) in an oralpharmaceutical formulation. The present disclosure is based upon thefinding that resistance to tramadol analgesia in subjects with reducedactivity of CYP2D6 (i.e., poor metabolizers or ‘PMs’) is overcome byadministering M1 and tramadol together, a synergistic combination ofagents for relieving a disorder modulated by opiate receptor activityand/or monoamine activity, and in particular for relieving acute,chronic and neuropathic pain. Without being bound by theory, the presentdisclosure is based upon the hypothesis that tramadol resistance in PMsis overcome when M1 and tramadol are administered together as a resultof supplementing these patients with the M1 metabolite that PM patientsare incapable of adequately generating on their own. By providing boththe M1 metabolite and tramadol, the entire spectrum of synergisticopioid and monoaminergic activity is restored in subjects with the PMphenotype. Advantageously, analgesia is also obtained when M1 andtramadol are administered together in subjects with genotypes notresistant to tramadol, and with fewer adverse events in subjects withthe UM phenotype.

This disclosure is also based upon the discovery that achieving optimalsynergy between tramadol and M1 in any subject is preferablyaccomplished with the M1 in a sustained release form, and the tramadolin an immediate-release or sustained release form. Without being boundby theory, in order to be effective in the treatment of a disordermodulated by opiate receptor activity and/or monoamine activity, and inparticular for relieving acute, chronic and neuropathic pain, it isnecessary that sufficient amounts of both M1 and tramadol are present,in particular in the concentrations and concentration ratios required toproduce this surprising synergistic effect.

These concentrations and concentration ratios are reflected in the bloodplasma levels of both these active ingredients. Maintaining said bloodplasma levels within a range of particular concentration ratios istherefore a desirable goal. It has been unexpectedly discovered however,that this goal is exceedingly challenging because of the very differenthalf-life of circulating M1 due to oral tramadol administration (i.e.,M1 arising from tramadol metabolism) compared to the half-life ofcirculating M1 due to the direct oral administration of M1 in animmediate-release form. Indeed, the clearance of M1 from the plasma dueto oral tramadol administration is relatively slow, while the clearanceof M1 due to oral dosing of M1 is relatively fast. Thus, without specialmeasures, the blood M1 plasma level after administering M1 and tramadoltogether, either as a single-dose are as dose cycles, will beinsufficient to be effective with plasma tramadol levels, and thesynergistic effect no longer present.

Thus, aspect of this disclosure provides a pharmaceutical compositionfor oral administration of O-desmethyltramadol. Preferably,O-desmethyltramadol is the 1R,2R-isomer or ‘(+)-M1’, the 1S,2S-isomer or‘(−)-M1’, or a racemic mixture of both isomers or ‘(+/−)-M1’.Preferably, the pharmaceutical composition is a tablet or capsule fororal administration. More preferably, the pharmaceutical compositioncomprises a sustained release delivery system of O-desmethyltramadol.Preferably, the amount of O-desmethyltramadol in the pharmaceuticalcomposition is from 5 mg to 100 mg. Preferably, the pharmaceuticalcomposition further comprises tramadol in an amount from 5 mg to 200 mg.In preferred embodiments the M1 salt is M1 HCl.

The present disclosure further provides a pharmaceutical compositioncomprising O-desmethyltramadol and tramadol, or a pharmaceuticallyacceptable salt thereof, wherein the O-desmethyltramadol and tramadolconcentrations are in a ratio of 95:5 to 5:95 by weightO-desmethyltramadol to tramadol, and more preferably 80:20 to 20:80,75:25 to 45:55, and in particular 20:2.5, 20:5.0, 20:7.5, 20:10,20:12.5, 20:15, 20:17.5, 20:20, 20:22.5 and 20:25.

In embodiments involving an oral dosage form of O-desmethyltramadol (M1)and tramadol, M1 is preferably provided in a sustained release dosageform and tramadol is provided as an immediate release dosage form (e.g.,each within discrete granules encompassed within the same capsule,wherein the M1 granules provide sustained release, or alternatively as amulti-layer tablet, wherein one layer provides sustained released andthe other layer provides immediate release). In other preferredembodiments of an oral dosage form, M1 and tramadol are both provided ina sustained release dosage form, wherein each form provides sustainedrelease with the same or different kinetics (e.g., each within sustainedrelease granules encompassed within the same capsule, or alternatively,both within the same monolithic sustained release tablet). The sustainedrelease dosage form thus comprises a substrate and a pharmaceuticallyeffective amount of M1 or tramadol or both, or pharmaceuticallyacceptable salts thereof, wherein the term ‘substrate’ refers to anymaterial or combination of materials, or forms thereof, that results inthe in vitro release (i.e., dissolution) pattern specified below for M1or tramadol or both.

In further embodiments the said substrate is a suitable matrix materialin which M1 or its salt form is incorporated, said matrix materialpreferably comprising polyvinyl acetate and polyvinylpyrrolidone andmixtures thereof, or alternatively, a hydrophilic swellable polymer suchas hydroxypropylmethyl cellulose and a salt (i.e., an ‘electrolyte’).

In a further aspect, the present pharmaceutical preparations comprisetwo or more phases. In certain embodiments, the respective major partsof M1 or its salt form, and of tramadol, are in different phases of thepharmaceutical preparations. In these embodiments at least one phase maycontain either the major part of tramadol or the major part of M1 or asalt-form thereof. In particular embodiments, one phase contains themajor part of M1 or a salt thereof and another phase contains the majorpart of tramadol. Further particular embodiments are pharmaceuticalpreparations that take the form of a biphasic tablet having a phase thatcomprises the major part of tramadol and another phase that comprisesthe major part of M1 or a salt form thereof. The phases in theseembodiments may take the form of layers.

In a specific aspect, an embodiment concerns pharmaceuticalpreparations, as described herein, comprising two or more phases,wherein M1 or its salt form and tramadol are in different phases of thepharmaceutical preparations. In particular embodiments, one phasecontains the M1 or a salt thereof and another phase contains thetramadol. Further particular embodiments are pharmaceutical preparationsthat take the form of a biphasic tablet having a first phase thatcomprises the tramadol active ingredient and a second phase thatcomprises the M1 active ingredient or a salt form thereof.

In a particular aspect the present disclosure provides pharmaceuticalpreparations as defined herein, wherein said preparations are bi- ormulti-layer tablets and wherein tramadol and M1, or a salt-form thereof,are localized exclusively to a layer. In particular embodiments, thepreviously mentioned pharmaceutical preparations take the form of abilayer tablet having a first phase that comprises the tramadol activeingredient and a second phase that comprises the M1 active ingredient ora salt form thereof.

In a further aspect, there is provided a bi- or multiphasic tabletcontaining an effective amount of tramadol having at least one phase orlayer that contains from about 20% to about 100%, in particular fromabout 30% to about 90% or from about 50% to 80% of polymeric matrixmaterial.

In a particular embodiment, the tablets are coated with an appropriatecoating. The coating may be for taste masking or for other purposes.

There is also provided pharmaceutical preparations, as defined herein,that are capsules or sachets. The tramadol and/or the M1 containingphase or phases in these embodiments may take the form of pellets.

There is further provided a process for manufacturing the oralpharmaceutical preparation described herein, comprising mixing M1 HCl,being incorporated in a suitable sustained release substrate, andtramadol, preferably formulated in a suitable solid carrier form.

There is further provided a process for manufacturing a bi- ormultiphasic tablet, comprising compressing two or more pre-shaped phasesin an appropriate compressing apparatus.

In a further aspect there is provided a process for manufacturing a bi-or multilayer tablet comprising compressing a suitable tramadolcontaining composition as to form a layer, laying M1 containing matrixmaterial on this tramadol containing layer, compressing the whole, andif desired laying further compositions of tramadol and/or further M1containing matrix material thereon and each time subjecting the whole toa compression and if further desired coating the thus prepared dosageform.

In a further aspect there is provided a process for manufacturing a bi-or multilayer tablet in accordance with the disclosure comprisingcompressing M1 containing matrix material as to form a layer, laying asuitable tramadol containing mixture on this M1 containing matrixmaterial layer, compressing the whole, and if desired laying furthercompositions of tramadol and/or further M1 matrix material thereon andeach time subjecting the whole to a compression and if further desiredcoating the thus prepared dosage form.

The present disclosure further provides a method for treating disordersmodulated by at least opiate receptor activity or monoamine activitycomprising orally administering to a mammal in need thereof atherapeutically effective amount of O-desmethyltramadol, or apharmaceutically acceptable salt thereof. The present disclosure furtherprovides a method for relieving acute and chronic pain, comprisingorally administering to a mammal in need thereof a therapeuticallyeffective amount of O-desmethyltramadol, or a pharmaceuticallyacceptable salt thereof. Preferably, the method further comprises orallyadministering tramadol, or a pharmaceutically acceptable salt thereof.Preferably, the amount of O-desmethyltramadol is 5 mg to 100 mg and theamount of tramadol is 5 mg to 200 mg. More preferably, the amount ofO-desmethyltramadol, or a pharmaceutically acceptable salt thereof is 10mg to 40 mg and the amount of tramadol, or a pharmaceutically acceptablesalt thereof is 10 mg to 40 mg.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A shows a graphical representation of plasma tramadolconcentrations in a subject after a single oral dose of IR forms of 100mg racemic tramadol (ULTRAM® tablets) and 20 mg and 40 mg racemicO-desmethyltramadol.

FIG. 1B shows a graphical representation of plasma O-desmethyltramadolconcentrations in the same subject as in FIG. 1A after a single oraldose of IR forms of 100 mg racemic tramadol (ULTRAM® tablets) and 20 mgand 40 mg racemic O-desmethyltramadol.

FIG. 2A shows a graphical representation of predicted (based onsingle-dose pharmacokinetic parameters) and actual plasmaO-desmethyltramadol concentrations in the subject after having received10 doses of 20 mg IR O-desmethyltramadol every 6 hours (9^(th) and10^(th) dose shown).

FIG. 2B shows the same plasma profile for the 20 mg O-desmethyltramadolIR formulation as in FIG. 1A vs. the plasma O-desmethyltramadolconcentrations in the same subject after having received 10 doses of 25,50, 75 or 100 mg IR tramadol (ULTRAM® tablets) every 6 hours (9^(th) and10^(th) dose shown).

FIG. 3 shows a graphical representation of the mean plasmaO-desmethyltramadol (M1) concentration as a function of dose of IRtramadol (ULTRAM® tablets) given every 6 hours for the 9^(th) and10^(th) dose data from FIG. 2 (i.e., mean M1 during hours 48-60 fromstart of dosing).

FIG. 4 shows a graphical representation of dissolution kinetics ofsustained release formulation SR100 as a function of pH.

FIG. 5A shows a graphical representation of dissolution data ofsustained release formulations SR100, SR101 and SR102.

FIG. 5B shows dissolution data of sustained release formulations SR103,SR104 and SR105 with a √t chart provided as the inset.

FIG. 6A shows a graphical representation of the dissolution data ofSR100, SR101 and SR102 (20 mg M1 HCl strength series) overplayed withthe dissolution data of SR103 (40 mg M1 HCl strength series).

FIG. 6B shows a graphical representation of the dissolution data ofSR100, SR101 and SR102 (20 mg M1 HCl strength series) overplayed withthe dissolution data of SR104 (40 mg M1 HCl strength series).

FIG. 6C shows a graphical representation of the dissolution data ofSR100, SR101 and SR102 (20 mg M1 HCl strength series) overplayed withthe dissolution data of SR105 (40 mg M1 HCl strength series).

FIG. 7 shows a graphical representation of the dissolution data ofsustained release formulation SR301 in media at pH 1.2 and 7.4 and thetramadol HCl extended release (ULTRAM ER®) control in a medium with pH7.4.

FIG. 8 shows a graphical representation of the dissolution data ofsustained release formulation SR302, SR303, SR304 and SR305. Alsorepresented is the dissolution data of the tramadol HCl extended release(ULTRAM ER®) control.

FIG. 9 shows a graphical representation of the dissolution data ofsustained release formulation SR302 in media at pH 1.2 and 7.4.

FIG. 10 shows a graphical representation of the dissolution data ofsustained release formulation SR306 and the tramadol HCl extendedrelease (ULTRAM ER®) control in a medium with pH 7.4.

FIG. 11 shows a graphical representation shows a graphicalrepresentation of the dissolution data of sustained release formulationSR307, SR308, SR309, SR310 and SR311.

FIG. 12 shows a graphical representation of dissolution kinetics ofsustained release formulation

FIG. 13A shows a graphical representation of plasma O-desmethyltramadol(M1) concentrations in a subject after a single oral dose of SR M1+IRtramadol combination form SR307+T₃, wherein SR307 is the SR M1 form-with40 mg M1 HCl, and T₃ is 30 mg of racemic tramadol IR (proportionalfraction of a 50 mg ULTRAM® tablet). The same control data for twosingle-dosings of 100 mg IR tramadol HCl (two 50 mg ULTRAM® tablets) areshown for comparison purposes.

FIG. 13B shows a graphical representation of plasma O-desmethyltramadol(M1) concentrations in a subject after a single oral dose of SR M1+IRtramadol combination SR105+T₃, wherein SR105 is the SR M1 form with 40mg M1 HCl, and T₃ is 30 mg of racemic tramadol IR (proportional fractionof a 50 mg ULTRAM® tablet). The same control data for two single-dosingsof 100 mg IR tramadol HCl (two 50 mg ULTRAM® tablets) are shown forcomparison purposes.

FIG. 14 shows a graphical representation of the fraction absorbed as afunction of the fraction released according to the IVIVC model developedherein for sustained release formulations SR103, SR104, SR105, SR203,SR206, SR307, SR308 and SR310.

FIG. 15A shows a graphical representation of the actual versusIVIVC-model-predicted M1 plasma concentration profiles for a single-doseof SR103 (monolithic CDT® series).

FIG. 15B shows a graphical representation of the actual versusIVIVC-model-predicted M1 plasma concentration profiles for a single-doseof SR104 (monolithic CDT® series).

FIG. 15C shows a graphical representation of the actual versusIVIVC-model-predicted M1 plasma concentration profiles for a single-doseof SR105 (monolithic CDT® series).

FIG. 16A shows a graphical representation of the actual versusIVIVC-model-predicted M1 plasma concentration profiles for a single-doseof SR203 (monolithic HPMC series).

FIG. 16B shows a graphical representation of the actual versusIVIVC-model-predicted M1 plasma concentration profiles for a single-doseof SR206 (monolithic HPMC series).

FIG. 17A shows a graphical representation of the actual versusIVIVC-model-predicted M1 plasma concentration profiles for a single-doseof SR307 (monolithic KOLLIDON® SR series).

FIG. 17B shows a graphical representation of the actual versusIVIVC-model-predicted M1 plasma concentration profiles for a single-doseof SR308 (monolithic KOLLIDON® SR series).

FIG. 17C shows a graphical representation of the actual versusIVIVC-model-predicted M1 plasma concentration profiles for a single-doseof SR310 (monolithic KOLLIDON® SR series).

FIG. 18 shows a graphical representation of the plasmaO-desmethyltramadol (M1) concentrations in the subject after havingreceived 10 doses of SR102 every 6 hours (9^(th) and 10^(th) dosesshown). Also reproduced from FIG. 2B for comparison purposes is the M1plasma profiles for 20 mg IR O-desmethyltramadol and 25, 50, 75 or 100mg IR tramadol (ULTRAM® tablets), all given every 6 hours (9^(th) and10^(th) doses shown for each).

FIG. 19 shows a graphical representation of the plasmaO-desmethyltramadol (M1) concentrations in the subject after havingreceived 10 doses every 6 hours (9^(th) and 10^(th) doses shown) of (i)one SR102 tablet plus 15 mg IR tramadol tablet (ULTRAM®), or (ii) twoSR102 tablets plus 30 mg IR tramadol tablet. Also reproduced from FIG.2B for comparison purposes is the M1 plasma profiles for 25, 50, 75 or100 mg IR tramadol (ULTRAM® tablets), all given every 6 hours (9^(th)and 10^(th) doses shown for each).

FIG. 20A shows the actual versus predicted average plasma levels for M1after SR M1 was given simultaneously with IR tramadol HCl as acombination formulation.

FIG. 20B shows the actual versus predicted average plasma levels fortramadol after SR M1 was given simultaneously with IR tramadol HCl as acombination formulation as in FIG. 20A.

DETAILED DESCRIPTION

This disclosure provides a pharmaceutical composition of the M1metabolite of tramadol (i.e., O-desmethyltramadol) in an oralformulation. This finding led to the additional discovery thatresistance to tramadol analgesia in subjects with reduced activity ofCYP2D6 (i.e., poor metabolizers or ‘PMs’) is overcome by administeringM1 and tramadol together, a synergistic combination of agents forrelieving a disorder modulated by opiate receptor activity and/ormonoamine activity, and in particular for relieving acute, chronic andneuropathic pain. Without being bound by theory, it is believed thattramadol resistance in PMs is overcome when M1 and tramadol areadministered together as a result of supplementing these patients withthe M1 metabolite that they are incapable of adequately generating ontheir own. By providing both the M1 metabolite and the parent drug, thetwo agents are able to act synergistically and the entire spectrum ofopioid and monoaminergic activity is restored in subjects with the PMphenotype. Advantageously, analgesia is also obtained when M1 andtramadol are administered together in subjects with genotypes notresistant to tramadol, and with fewer adverse events in subjects withthe UM phenotype.

The present disclosure provides tramadol and its primary metabolite,O-desmethyltramadol (M1). Tramadol and O-desmethyltramadol (M1) eachexist as the trans conformational isomer, with each conformationalisomer existing as a pair of enantiomers because two chiral centers arepresent in the cyclohexane ring of each compound. Accordingly, tramadoland O-desmethyltramadol each consist of an enantiomeric pair, designated(1R,2R)-tramadol, (1S,2S)-tramadol, (1R,2R)—O-desmethyltramadol, and(1S,2S)—O-desmethyltramadol.

As used herein, the terms ‘tramadol’, ‘O-desmethyltramadol’ and ‘M1’unless specified otherwise, shall mean the racemic mixture of the1R,2R-isomer and the 1S,2S-isomer. As used herein, the terms ‘tramadolspecies’ or ‘O-desmethyltramadol species’ shall mean the racemate, the1R,2R-isomer or 1S,2S-isomer of tramadol or 0-desmethyltramadol,respectively.

In preferred embodiments, a combination of O-desmethyltramadol andtramadol is provided. In certain embodiments, the combination comprisesO-desmethyltramadol and tramadol in a weight ratio range of 95:5 to5:95. A weight ratio range of 80:20 to 20:80 is preferred. Otherpreferred weight ratios of O-desmethyltramadol to tramadol include90:10, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, 20:80 and 10:90. For200 mg of the combination, the above weight ratios provideO-desmethyltramadol and tramadol in amounts of (mg:mg) 180:20, 160:40,140:60, 120:80, 100:100, 80:120, 60:140, 40:160 and 20:180. For 100 mgof the combination, the above weight ratios provide O-desmethyltramadoland tramadol in amounts of (mg:mg) 90:10, 80:20, 70:30, 60:40, 50:50,40:60, 30:70, 20:80 and 10:90. For 50 mg of the combination, theseweight ratios provide O-desmethyltramadol and tramadol in amounts of(mg:mg) 45:5, 40:10, 35:15, 30:20, 25:25, 20:30, 15:35, 10:40 and 5:45.

Other preferred weight ratios of O-desmethyltramadol to tramadol include20:7.5, 20:10, 20:12.5, 20:15, 20:17.5, 20:20, 20:22.5 and 20:25. For acombination tablet containing 20 mg O-desmethyltramadol, the aboveweight ratios provide O-desmethyltramadol and tramadol in amounts of(mg:mg) 20:7.5, 20:10, 20:12.5, 20:15, 20:17.5, 20:20, 20:22.5 and20:25. For a combination tablet containing 40 mg O-desmethyltramadol,the above weight ratios provide O-desmethyltramadol and tramadol inamounts of (mg:mg) 40:15, 40:20, 40:25, 40:30, 40:35, 40:40, 40:45 and40:50.

The present disclosure further provides eight additional combinations,including: (1) racemic O-desmethyltramadol with (1R,2R)-tramadol; (2)racemic O-desmethyltramadol with (1S,2S)-tramadol; (3)(1R,2R)—O-desmethyltramadol with racemic tramadol; (4)(1S,2S)—O-desmethyltramadol with racemic tramadol; (5)(1R,2R)—O-desmethyltramadol with (1R,2R)-tramadol; (6)(1R,2R)—O-desmethyltramadol with (1S,2S)-tramadol; (7)(1S,2S)—O-desmethyltramadol with (1R,2R)-tramadol; and (8)(1S,2S)—O-desmethyltramadol with (1S,2S)-tramadol. In these embodiments,the weight ratio range for the racemate to isomer, isomer to racemate,or isomer to isomer is a weight ratio range of 95:5 to 5:95 forO-desmethyltramadol:tramadol species. Preferred weight ratios forO-desmethyltramadol:tramadol species include 90:10, 80:20, 70:30, 60:40,50:50, 40:60, 30:70, 20:80 and 10:90. For 200 mg of the combination, theabove weight ratios provide O-desmethyltramadol and tramadol species inamounts of (mg:mg) 180:20, 160:40, 140:60, 120:80, 100:100, 80:120,60:140, 40:160 and 20:180. For 100 mg of the combination, the aboveweight ratios provide O-desmethyltramadol and tramadol species inamounts of (mg:mg) 90:10, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70,20:80 and 10:90. For 50 mg of the combination, these weight ratiosprovide O-desmethyltramadol and tramadol species in amounts of (mg:mg)45:5, 40:10, 35:15, 30:20, 25:25, 20:30, 15:35, 10:40 and 5:45.

O-desmethyltramadol (M1) is useful for treating disorders modulated byopiate receptor activity or monoamine activity, or both opiate receptoractivity and monoamine activity. Accordingly, this disclosure providesmethods for such treatment. This disclosure provides a method fortreating disorders modulated by opiate receptor activity or monoamineactivity, or both opiate receptor activity and monoamine activity,comprising administering to a mammal in need thereof a therapeuticallyeffective amount of O-desmethyltramadol, or a pharmaceuticallyacceptable salt thereof. The O-desmethyltramadol administered may be(1R,2R)—O-desmethyltramadol, (1S,2S)—O-desmethyltramadol, or a racemicmixture thereof. In some embodiments, the amount of O-desmethyltramadolspecies administered is 5 mg to 200 mg, 5 mg to 100 mg, 5 mg to 50 mg, 5to 25 mg, and more preferably 20 mg to 50 mg. In other embodiments, theamount of O-desmethyltramadol species administered is 5, 10, 15, 20, 25,30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100 mg.Preferred amounts of O-desmethyltramadol species administered are 20,25, 30, 35, 40, 45 and 50 mg. Administration is preferably via the oralroute.

As used herein, the terms ‘mammal’, ‘subject’ or ‘patient’ are usedinterchangeably and are intended to have equivalent meanings.

In a preferred embodiment, particularly those involving the treatment ofacute and chronic pain, is a method for administrating to a subjectO-desmethyltramadol together with tramadol, or a pharmaceuticallyacceptable salt of both or either. The O-desmethyltramadol administeredis, for example, (1R,2R)—O-desmethyltramadol,(1S,2S)—O-desmethyltramadol, or the racemic mixture thereof, and thetramadol administered may be (1R,2R)-tramadol, (1S,2S)-tramadol, or theracemic mixture thereof. Such methods are particularly preferred insubjects who are ‘poor metabolizers’ of tramadol to O-desmethyltramadol,particularly those with a genotype resulting in reduced activity ofCYP2D6. Such methods are also preferred in subjects who are ‘ultra-rapidmetabolizers’ of tramadol to O-desmethyltramadol, particularly thosewith a genotype resulting in abnormally high activity of CYP2D6. Theterms ‘poor metabolizers’ and ‘ultra-rapid metabolizers’ of tramadol aredefined in the art; see for example Kirchheiner et al. and thereferences therein (Kirchheiner et al., “Effects of the CYP2D6 geneduplication on the pharmacokinetics and pharmacodynamics of tramadol” J.Clin. Psychopharmacol., 2008. 28(1): p. 78-83). With respect to CYP2D6genotypes, the human population has generally been subdivided into thefollowing categories: poor metabolizer (‘PM’, two inactive alleles, +10%of population), intermediate metabolizer (‘IM’, one inactive allele, 35%of population), extensive or ‘normal’ metabolizer (‘EM’, two activealleles, 50%) and ultra-rapid metabolizer (‘UM’, gene duplicationsyielding more than two active alleles, 2% in northern European whitesand 7% in southern Europe). The in vivo production in humans of bothenantiomers of M1 (i.e., 1R,2R—O-desmethyltramadol or ‘(+)-M1’, and1S,2S—O-desmethyltramadol or ‘(−)-M1’) from racemic tramadol isdependent on the polymorphic isoenzyme of the debrisoquine-type,cytochrome P450 2D6 (CYP2D6). Methods for administratingO-desmethyltramadol together with tramadol are provided herein, whereinthe amount of O-desmethyltramadol is 5 mg to 100 mg and the amount oftramadol is 5 mg to 200 mg. In preferred embodiments, the amount ofO-desmethyltramadol or a pharmaceutically acceptable salt thereof is 10mg to 50 mg, and the amount of tramadol or a pharmaceutically acceptablesalt thereof is 10 mg to 100 mg. Preferably, the O-desmethyltramadol andtramadol are each the racemate, but the isolated isomers are alsosuitable according to the disclosure.

In methods for administrating O-desmethyltramadol together withtramadol, any weight ratio of O-desmethyltramadol:tramadol specieswithin the range of 95:5 to 5:95 is encompassed by the disclosure.Preferred weight ratios of O-desmethyltramadol:tramadol species include90:10, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, 20:80 and 10:90. Aweight ratio range of 80:20 to 20:80 is preferred, and more preferably75:25 to 45:55, and in particular the ratios 20:7.5, 20:10, 20:12.5,20:15, 20:17.5, 20:20, 20:22.5 and 20:25 are preferable.

For a combined 200 mg weight of O-desmethyltramadol and tramadolspecies, the above ratios provide O-desmethyltramadol:tramadol speciesin amounts including but not limited to (mg:mg) 180:20, 160:40, 140:60,120:80, 100:100, 80:120, 60:140, 40:160 and 20:180. For a combined 100mg weight of O-desmethyltramadol:tramadol species, the above ratiosprovide O-desmethyltramadol and tramadol species in amounts includingbut not limited to (mg:mg) 90:10, 80:20, 70:30, 60:40, 50:50, 40:60,30:70, 20:80 and 10:90. For a combined 50 mg weight ofO-desmethyltramadol and tramadol species, these ratios provideO-desmethyltramadol:tramadol species in amounts including but notlimited to (mg:mg) 45:5, 40:10, 35:15, 30:20, 25:25, 20:30, 15:35, 10:40and 5:45. For a combination tablet containing 20 mg O-desmethyltramadol,the above weight ratios provide O-desmethyltramadol and tramadol inamounts including but not limited to (mg:mg) 20:7.5, 20:10, 20:12.5,20:15, 20:17.5, 20:20, 20:22.5 and 20:25. For a combination tabletcontaining 40 mg O-desmethyltramadol, the above weight ratios provideO-desmethyltramadol and tramadol in amounts including but not limited to(mg:mg) 40:15, 40:20, 40:25, 40:30, 40:35, 40:40, 40:45 and 40:50.

As used herein, the term “disorder” modulated by opiate receptoractivity and/or monoamine activity refers to a disorder, disease orcondition where modulating opiate receptor activity and/or monoamineactivity is an effective means of alleviating the disorder or one ormore of the biological manifestations of the disease or disorder; orinterferes with one or more points in the biological cascade leading tothe disorder or responsible for the underlying disorder; or alleviatesone or more symptoms of the disorder. Thus, disorders subject tomodulation include those for which:

(a) the lack of opiate receptor activity and/or monoamine activity is acause of the disorder or one or more of the biological manifestations,whether the activity was altered genetically, by infection, byirritation, by internal stimulus or by some other cause;

(b) the disease or disorder or the observable manifestation ormanifestations of the disease or disorder are alleviated by opiatereceptor activity and/or monoamine activity. The lack of opiate receptoractivity and/or monoamine activity need not be causally related to thedisease or disorder or the observable manifestations thereof, or

(c) opiate receptor activity and/or monoamine activity interferes withpart of the biochemical or cellular cascade that results in or relatesto the disease or disorder. In this respect, the opiate receptoractivity and/or monoamine activity alters the cascade, and thus controlsthe disease, condition or disorder.

Disorders modulated by opiate receptor activity and/or monoamineactivity include acute and chronic pain, neuropathic pain, affectivedisorders, including depression and anxiety, behavioral disorders,including attention deficit disorders, eating disorders, cerebralfunction disorders, substance abuse, urinary incontinence and prematureejaculation as those terms are defined in U.S. Pat. Nos. 6,780,891,6,660,774 and 6,974,839, incorporated by reference herein. The term“neuropathic pain” is applied to any acute or chronic pain syndrome inwhich the sustaining mechanism for the pain is believed to involveabnormal transmission (peripheral) or processing (central) ofsomatosensory input.

The present disclosure relates to a method for relieving a disordermodulated by opiate receptor activity and/or monoamine activity. Mostpreferably, the disorder is acute pain, chronic pain or neuropathicpain. The method comprises orally administering to a mammal in needthereof a therapeutically effective amount of O-desmethyltramadol (M1),or a pharmaceutically acceptable salt thereof. In a preferredembodiment, the method comprises orally administering to a mammal inneed thereof a therapeutically effective amount of O-desmethyltramadol(M1) and tramadol, or pharmaceutically acceptable salts thereof.

The present disclosure also provides a pharmaceutical compositioncontaining a therapeutically effective amount of an O-desmethyltramadolspecies, or a pharmaceutically acceptable salt thereof. Apharmaceutically acceptable carrier may also be included. Apharmaceutical composition adapted for the oral delivery of anO-desmethyltramadol species is particularly preferred. Other therapeuticingredients may also be included. A preferred therapeutic ingredient isa therapeutically effective amount of a tramadol species, or apharmaceutically acceptable salt thereof. The pharmaceuticalcompositions contain O-desmethyltramadol and optional tramadol species,or their pharmaceutically acceptable salts, in amounts and in weightratios as provided in this disclosure (vide supra).

The term “pharmaceutically acceptable salts” mean salts prepared frompharmaceutically acceptable non-toxic acids including inorganic acidsand organic acids. Examples of acids that form pharmaceuticallyacceptable salts with tramadol and O-desmethyltramadol species includeacetic acid, benzenesulfonic (besylate) acid, benzoic acid,camphorsulfonic acid, citric acid, ethenesulfonic acid, fumaric acid,gluconic acid, glutamic acid, hydrobromic acid, hydrochloric acid,isethionic acid, lactic acid, maleic acid, malic acid, mandelic acid,methanesulfonic acid, mucic acid, nitric acid, pamoic acid, pantothenicacid, phosphoric acid, succinic acid, sulfuric acid, tartaric acid andp-toluenesulfonic acid. The hydrochloric acid salt is particularlypreferred.

Any suitable route of administration may be employed for providing thepatient with an effective dosage of O-desmethyltramadol and optionaltramadol species, or their pharmaceutically acceptable salts. Forexample, oral, rectal, parenteral (including subcutaneous,intramuscular, and intravenous) routes may be employed. Dosage formsinclude tablets, troches, dispersions, suspensions, solutions, capsulesand patches. In particular, the composition may be formulated for oraladministration, and may be in the form of a tablet or capsule.

Pharmaceutically acceptable carriers for use in the compositions of thepresent disclosure may take a wide variety of forms, depending on theforms preparation desired for administration, for example, oral orparenteral (including intravenous). In preparing the composition fororal dosage form, any of the usual pharmaceutical media may be employed,such as, water, glycols, oils, alcohols, flavoring agents,preservatives, and coloring agents in the case of oral liquidpreparation, including suspension, elixirs and solutions. Carriers suchas starches, sugars, microcrystalline cellulose, diluents, granulatingagents, lubricants, binders and disintegrating agents may be used in thecase of oral solid preparations such as powders, capsules and caplets,with the solid oral preparation being preferred over the liquidpreparations. Preferred solid oral preparations are tablets or capsules,because of their ease of administration. If desired, tablets may becoated by standard aqueous or nonaqueous techniques. Oral and parenteralsustained release dosage forms may also be used.

Oral syrups, as well as other oral liquid formulations, are well knownto those skilled in the art, and general methods for preparing them arefound in any standard pharmacy school textbook, for example Remington:The Science and Practice of Pharmacy. Chapter 86 of the 19^(th) editionof Remington entitled “Solutions, Emulsions, Suspensions and Extracts”describes in complete detail the preparation of syrups (pages 1503-1505)and other oral liquids. Similarly, sustained (i.e., controlled) releaseformulations are well known in the art, and Chapter 94 of the samereference, entitled “Sustained-Release Drug Delivery Systems,” describesthe more common types of oral and parenteral sustained-release dosageforms (pages 1660-1675). The relevant disclosure, Chapters 84 and 96, isincorporated herein by reference. Because they reduce peak and troughplasma concentrations, as compared to conventional immediate release(IR) oral dosage forms, sustained release dosage forms are particularlyuseful for providing a therapeutic plasma concentration ofO-desmethyltramadol while (i) avoiding the side effects associated withhigh peak plasma concentrations, and/or (ii) with respect to low troughO-desmethyltramadol plasma concentrations that occur with IR dosageforms, avoid a lack of synergy with tramadol or lack of efficacyaltogether.

The term ‘immediate release’ or ‘IR’ shall mean that the dosage formyields a dissolution or disintegration time of less than about 90, 60,30 or 20 minutes (preferably 20 minutes) (85% or more dissolving ordisintegrating) when tested according to USP 28 <701>, USP 28<711> orthe method in the online FDA CDER method database for the particularcommercial formulation. As used herein, ‘immediate release’ shall alsoencompass formulations wherein the active ingredient is fullysolubilized, where the dissolution time is zero by definition. As usedherein, the term ‘sustained release’ or ‘SR’ shall mean that the dosageform yields a dissolution or disintegration time longer than would berequired to meet the definition of immediate release.

In embodiments involving an oral dosage form of O-desmethyltramadol andtramadol, O-desmethyltramadol is preferably provided in a sustainedrelease dosage form and tramadol is provided as an immediate releasedosage form (e.g., each within discrete granules encompassed within thesame capsule, wherein the O-desmethyltramadol granules provide sustainedrelease, or alternatively as a multi-layer tablet, wherein one layerprovides sustained released and the other layer provides immediaterelease). In other preferred embodiments of an oral dosage form,O-desmethyltramadol and tramadol are both provided in a sustainedrelease dosage form, wherein each form provides sustained release withthe same or different kinetics (e.g., each within sustained releasegranules encompassed within the same capsule, or alternatively, bothwithin the same monolithic sustained release tablet). The sustainedrelease dosage form thus comprises a substrate and a pharmaceuticallyeffective amount of O-desmethyltramadol or tramadol or both, orpharmaceutically acceptable salts thereof, wherein the term ‘substrate’refers to any material or combination of materials, or forms thereof,that results in the in vitro release (i.e., dissolution) patternspecified below for O-desmethyltramadol or tramadol or both.

In still other preferred embodiments, the sustained release or immediaterelease dosage forms will contain an additional active ingredient, forexample, selected from the group consisting of acetaminophen, aspirin,ibuprofen, diclofenac, naproxen, indomethacin, fenoprofen, oxycodone,hydromorphone, codeine, hydrocodone and topiramate as provided in U.S.patent application Ser. Nos. 10/538,946, 12/252,117, 12/298,922,12/604,560, 12/644,444 and U.S. Pat. Nos. 5,336,691, 5,516,803,5,968,551 and 7,906,141, the disclosures of which are incorporated byreference herein.

A sustained release oral dosage form comprising a substrate comprising apharmaceutically effective amount of O-desmethyltramadol or apharmaceutically acceptable salt thereof (i.e., the active ingredient),will have a dissolution profile (i.e., rate) in vitro when measuredusing the USP Apparatus I Basket Method at 75 rpm in 900 ml 0.05 Mphosphate buffer with a pH 7.2 at 37° C. of:

between 15 and 74% O-desmethyltramadol released after 1 hour;

between 28 and 91% O-desmethyltramadol released after 2 hours;

between 38 and 101% O-desmethyltramadol released after 3 hours;

between 47 and 105% O-desmethyltramadol released after 4 hours;

between 59 and 105% O-desmethyltramadol released after 6 hours;

between 68 and 105% O-desmethyltramadol released after 8 hours;

between 75 and 105% O-desmethyltramadol released after 10 hours;

between 79 and 105% O-desmethyltramadol released after 12 hours;

about 100% O-desmethyltramadol released after 24 hours; by weight, saidsustained release oral dosage form providing a therapeutic effect forabout 6 to about 12 hours after oral administration and suitable fordosing every 6 to 24 hours. The term ‘suitable for dosing every 6 to 24hours’ means that the dosage forms are such that they can beadministered every 6 to 24 hours and give effective blood plasmaconcentrations of O-desmethyltramadol, or optionally O-desmethyltramadoland tramadol, such that they are effective to treat acute, chronic andneuropathic pain, and more generally, are effective for relieving adisorder modulated by opiate receptor activity and/or monoamineactivity. The sustained release oral dosage forms can be dosed every 24hours but also can be dosed differently, e.g., every 12 hours (b.i.d.)or every 6 hours (q.i.d.).

In a preferred embodiment there is provided a sustained release oraldosage form as defined above that will have a dissolution profile, asmeasured using the method defined above, as follows:

between 21 and 72% O-desmethyltramadol released after 1 hour;

between 34 and 89% O-desmethyltramadol released after 2 hours;

between 44 and 99% O-desmethyltramadol released after 3 hours;

between 52 and 105% O-desmethyltramadol released after 4 hours;

between 65 and 105% O-desmethyltramadol released after 6 hours;

between 70 and 105% O-desmethyltramadol released after 8 hours;

between 81 and 105% O-desmethyltramadol released after 10 hours;

between 86 and 105% O-desmethyltramadol released after 12 hours;

about 100% O-desmethyltramadol released after 24 hours; by weight.

In a more preferred embodiment there is provided a sustained releaseoral dosage form as defined above that will have a dissolution profile,as measured using the method defined above, as follows:

between 25 and 54% O-desmethyltramadol released after 1 hour;

between 40 and 69% O-desmethyltramadol released after 2 hours;

between 52 and 82% O-desmethyltramadol released after 3 hours;

between 61 and 92% O-desmethyltramadol released after 4 hours;

between 78 and 101% O-desmethyltramadol released after 6 hours;

between 83 and 105% O-desmethyltramadol released after 8 hours;

between 89 and 105% O-desmethyltramadol released after 10 hours;

between 91 and 105% O-desmethyltramadol released after 12 hours;

about 100% O-desmethyltramadol released after 24 hours; by weight.

In a most preferred embodiment there is provided a sustained releaseoral dosage form as defined above that will have a dissolution profile,as measured using the method defined above, as follows:

between 25 and 35% O-desmethyltramadol released after 1 hour;

between 40 and 50% O-desmethyltramadol released after 2 hours;

between 52 and 62% O-desmethyltramadol released after 3 hours;

between 61 and 71% O-desmethyltramadol released after 4 hours;

between 78 and 88% O-desmethyltramadol released after 6 hours;

between 83 and 93% O-desmethyltramadol released after 8 hours;

between 89 and 99% O-desmethyltramadol released after 10 hours;

between 91 and 105% O-desmethyltramadol released after 12 hours;

about 100% O-desmethyltramadol released after 24 hours; by weight.

In embodiments of an oral dosage form wherein O-desmethyltramadol andtramadol are both provided in a sustained release dosage form, thedissolution rate of tramadol will fall within the same % ranges as afunction of time as defined above for 0-desmethyltramadol. In apreferred embodiment, O-desmethyltramadol and tramadol will be in thesame sustained release oral dosage form together, and will havesubstantially the same dissolution kinetics (i.e., the ‘same dissolutionkinetics’ shall mean the difference between the % O-desmethyltramadoland % tramadol released at a given time point will be less than or equalto 10% and more preferably 5%).

As mentioned above, in order to act synergistically, the ratios of theblood plasma levels of tramadol:M1 should be within certain ranges andin particular the blood plasma levels of these ingredients should be inthe range of about 0.4:1 to about 33:1, in particular from about 0.4:1to about 6:1 of tramadol:M1, and from about 0.5:1 to 2.0:1 oftramadol:M1. An optimum ratio for these ingredients is about 0.5:1 to2.0:1 tramadol:M1. It further has been found that when M1 is released invitro in the quantities outlined above, upon multiple administrationsduring specific periods of time, e.g., every 24 hours, or, which ispreferred, every 6 hours, the plasma concentrations of M1 in vivo reacha steady-state and are constant within certain ranges during an extendedperiod of time. It has additionally been found that in pharmaceuticalpreparations as described herein, containing M1 or a salt thereof andtramadol, when the release of M1 follows the release pattern as outlinedabove, the ratio of the plasma concentrations of tramadol vis a vis M1is constant within certain ranges. This ratio has been found toapproximate 0.5:1 to 2.0:1 (w/w) or upon selection of the appropriateconcentrations of the tramadol and M1, or its salt form, and of thesubstrate and other carriers in a pharmaceutical dosage form, this ratiomay be about 0.5:1 to 2.0:1. This equally means that upon multipleadministrations of the pharmaceutical preparations herein, also duringspecific periods of time, e.g., every 24 hours, or, which is preferred,every 6 hours, the plasma concentrations of tramadol in vivo reach asteady-state and are constant within certain ranges during a long periodof time. The above findings related to blood plasma levels of tramadoland M1 allow both agents to act synergistically in any subjectirrespective of their CYP2D6 genotype, and therefore be effective intreating a disorder modulated by opiate receptor activity and/ormonoamine activity, including acute, chronic and neuropathic pain, inany subject. Further, subjects with the UM phenotype will experiencefewer adverse events.

As used herein, ‘constant within certain ranges’ means that there can befluctuations of the M1 or tramadol plasma concentrations, or of theabove stated ratio of the M1:tramadol plasma concentrations within anacceptable range, e.g., within 100% in particular, within 75%, furtherin particular within 50%. Alternatively, fluctuation of M1 or tramadolplasma concentrations can be expressed by the steady-state ‘fluctuationindex’ which is defined as follows: F_(i)=[Css_(max)−Css_(min)]/CSS_(Av)wherein F_(i) is the fluctuation index, Css_(max) the maximal plasmaconcentration at steady-state, Css_(min) the minimal plasmaconcentration at steady-state, and C_(AV) the average plasmaconcentration at steady-state, where C_(Av)=(CSS_(max)+CSS_(min))/2. Thefluctuation index can vary but for example is 40% to 50%, 50% to 60%,60% to 80% and 80% to 110%.

The in vitro dissolution profiles of M1 and tramadol outlined above aresupported by an in vitro/in vivo correlation (IVIVC) model thatcorrelates plasma M1 concentrations and the in vitro release of M1 andtramadol from immediate-release and sustained-release dose forms.Administration of an effective amount of M1 or tramadol will show aparticular course of M1 plasma concentrations. Ideally, plasma tramadolshould follow the same course as M1 so that the ratio of the plasmaconcentrations of both agents remains more or less constant, althoughthis is not essential. By consulting the IVIVC model of M1 and tramadolit has been found that it is possible to predict which plasma M1concentration profile correlates with a given in vitro release profileand vice versa (i.e., a reversed IVIVC). The latter allows a reversecalculation of the in vitro release profile that would cause aparticular in vivo plasma M1 profile.

Typically, the pharmaceutical preparations comprise M1 or its salt formin a suitable sustained release form, which may be any form that affordsrelease of M1 within the ranges specified above.

In certain embodiments, the preparations comprise sustained releaseforms wherein the M1 or its salt form is incorporated in a suitablematrix, which may be a sustained release matrix or a normal releasematrix having a sustained release coating. The sustained release formmay take various forms, e.g., particles of different sizes, pellets (orbeads), tablets, phases within a larger unit such as layers or sectionsof other shape within a larger unit (e.g., as in a multi-layer or abull-eye tablet). A number of such formats as well as the unit dosageforms in which these can be incorporated will be outlined in more detailhereinafter.

As used herein the term ‘phase’ refers to a defined three dimensionallyshaped section in a tablet dosage form that contains the same materialand wherein each phase is separated from the other. Examples of phasesare layers, which are incorporated in bi- or multi-layer tablets. Otherexamples are cylindrical, spherical or other tri-dimensionally shapedsections that can be present in tablets. This gives rise to differenttablet formats such as the so-called ‘bull-eye’ tablets, or concentrictablets (a central cylindrically shaped section completely surroundedwith one or more further cylindrical layers (i.e., a ring-likecombination), or ‘coated’ tablets wherein the coating is a layercompletely surrounding a tablet nucleus and the like tablet formats.Preference is given to bi- or multi-layer tablets.

Preferred embodiments are tablets that contain at least two phases, inparticular tablets that contain at least two layers.

In particular embodiments, the major part of the M1 or its salt form andof the tramadol are in different phases of the said pharmaceuticalpreparations. In said embodiments, an at least one phase may containeither the major part of tramadol or the major part of M1 or a salt-formthereof. In particular embodiments, one phase contains the major part ofM1 or a salt thereof and another phase contains the major part oftramadol.

As used herein, ‘major part’ means that the major quantity of the M1 orits salt form or of tramadol is present in a particular phase.Preferably the term ‘major part’ refers to a situation where at leastmore than about 90% of the concerned active ingredient is present in aparticular phase, for example more than 95%, or more than 98%, or morethan 99%, or even more than 99.5%. The same applies to the situationtake particular forms such as layers.

Most preferably a phase containing one of both active ingredients shouldcontain only a minute amount of the other active ingredient, or evennone of the other active ingredient, for example a phase may containtramadol and a minute amount, e.g., less than 1%, or less than 0.5% ofM1 or a salt form thereof, or vice versa.

Preferably a phase comprising M1 or a salt form thereof is adjacent to aphase containing tramadol.

Of particular interest are tablets that are biphasic, the latter beingpreferred, or multiphasic, e.g., having 3, 4, 5 or more phases. At leastone layer should comprise M1 or a salt form thereof but in case ofmultiphasic tablets, more than one layer comprising M1 or a salt formcan be present. Of still further interest are those preparations inwhich one or more of the phases are layers.

Particularly preferred embodiments are tablets wherein tramadol ispresent in amounts from about 10 mg to 500 mg tramadol per unit,preferably from about 25 mg to about 200 mg of tramadol per unit, e.g.,tablets having 25, 50, 100 or 200 mg per unit.

In a particular aspect, the tablets contain an effective amount oftramadol, wherein the tablets have at least one layer that contains fromabout 20% to about 100%, in particular from about 30% to about 90% orfrom about 50% to 80% of polymeric matrix material. The hygroscopicmatrix material containing layer may contain other ingredients such asthe ingredients mentioned hereinafter.

Formulations suitable for providing sustained release ofO-desmethyltramadol and immediate release of tramadol, or the sustainedrelease of both O-desmethyltramadol and tramadol are provided in U.S.patent application Ser. Nos. 12/225,498, 12/252,117, 12/298,922,12/336,495, 12/406,272, 12/604,560, 12/644,444 and U.S. Pat. Nos.5,427,799, 5,580,578, 5,591,452, 6,090,411, 6,143,327, 6,245,357,6,254,887, 7,074,430, 7,611,730 and 7,906,141 the disclosures of whichare incorporated by reference herein. The sustained release preparationshould release O-desmethyltramadol, and optionally tramadol, in vitro inthe quantities outlined above. In some embodiments, these are obtainedby measurement using the USP Apparatus I Basket Method at 75 rpm in 900ml 0.05 M phosphate buffer with a pH 7.2 at 37° C. and usingspectrophotometry at an appropriate detection wavelength, e.g., at 270nm in the case of O-desmethyltramadol and tramadol. Release of theactive ingredients can also be measured in situ with a fiber opticdissolution system, using the second derivative correction method at asuitable wavelength range, which, in case of tramadol is in the range of283 to 289 nm. Alternatively, release of O-desmethyltramadol andtramadol from a combination dosage form (i.e., both in one SR form, eachin a different SR form, or one in an SR and the other in an IR form) canbe separately measured using high performance liquid chromatography(HPLC) and a suitable detection system such as, for example, UVdetection at an appropriate wavelength (e.g., at 274, 272 or 271 nm fortramadol HCl, M1 HCl and M1 free base, respectively), or with arefractive index detector.

In general, sustained release may be achieved using any of three broadcategories of delivery: (1) sustained release from a matrix, (2)sustained release from a reservoir and (3) sustained release fromcoated-beads and multi-particulates.

Sustained Release from a Matrix.

Where the matrix is a sustained release it may comprise suitabledigestible hydrophilic or hydrophobic polymeric or non-polymericmaterials.

Examples of such polymeric materials are hydrophilic or hydrophobicpolymers, such as polysaccharides, in particular gums (further inparticular pH dependent gums), cellulose ethers, especiallyalkylcelluloses, in particular C₁-C₆ alkyl cellulose, especially ethylcellulose, acrylic resins, protein-derived materials, polyalkyleneglycols, polysaccharide gums such as xanthan gum, and the like.Preferred are polymers such as polyvinyl acetate andpolyvinylpyrrolidone and mixtures thereof, in particular the mixtureknown as KOLLIDON® SR which is polyvinyl acetate (8 parts w/w) andpolyvinylpyrrolidone (2 parts w/w).

Examples of non-polymeric materials that can be used are digestiblelipids having a long chain alkyl moiety, which may be straight orbranched, saturated or unsaturated, substituted or unsubstituted. Ofparticular interest are C₈₋₅₀, especially C₁₂₋₄₀ lipids. Examplescomprise fatty acids, fatty alcohols, glyceryl esters of fatty acids,mineral and vegetable oils and waxes. Lipids having a melting point ofbetween 25 and 90° C. are preferred.

The sustained release form may conveniently contain between 1% and 90%,in particular from 10% to 90%, further in particular from 20% to 80% (byweight) of one or more hydrophilic or hydrophobic polymers or digestiblelipids. In embodiments where the polymeric material is a mixture ofpolyvinyl acetate and polyvinylpyrrolidone and mixtures such asKOLLIDON® SR or a polysaccharide gum such as xanthan gum, alginate orgum Arabic, the preparation may contain between 20% and 90%, inparticular from 30% to 80% (by weight). As used herein, ‘alginate’refers to alginate or its salts, in particular to its alkali metal saltssuch as sodium or potassium salts. In embodiments containingpolyalkylene glycols, the preparation may in particular contain up to60% (by weight) of one or more polyalkylene glycols. In furtherparticular embodiments, the preparation may contain up to 60% (byweight) of at least one digestible, long chain lipid.

Of interest are sustained release matrixes comprising xanthan gumoptionally in mixture with other gums, in particular with other pHdependent gums such as, for example, alginate.

Optionally, the sustained release matrix may also contain otherpharmaceutically acceptable ingredients which are conventional in thepharmaceutical art such as diluents (in particular lactose), lubricants,binders, granulating aids, colorants, flavorants, surfactants, pHadjusters, anti-adherents and glidants (e.g., colloidal silica), andplasticizers (e.g., dibutyl sebacate) and other suitable ingredients(e.g., ammonium hydroxide, oleic acid). Preferred are ingredientsdescribed in U.S. Pat. No. 6,090,411 that further control the rate ofmatrix erosion through changes in gel thickness, electrolyte ionization,and ionic interactions (i.e., CDT® technology).

The sustained release form may conveniently be film coated using anyfilm coating material conventional in the pharmaceutical art. A filmcoat is added e.g., as a finish, for coloring purposes or taste maskingor a combination of these. Preferably an aqueous film coating is used.

Alternatively, the sustained release form may comprise an immediate orsustained release matrix, as a core, and further having a controlledrelease coating. In such embodiments the immediate release core may beprepared via art known procedures, e.g., by a suitable granulationprocess followed by compression, or by direct compression, followed by acoating step with a coating material that ensures controlled release. Insuch preparations, the immediate release section or core of thepreparation may contain any of the usual ingredients usually employed tomake such immediate release sections or cores. Any of the ingredientsmentioned herein with respect to carriers used for immediate releaseforms can be conveniently employed. In the case of a sustained releasecore, such embodiments may be prepared via the methods herein, followedby a coating step with a coating material that ensures controlledrelease.

The sustained release profile of O-desmethyltramadol and optionally alsotramadol can be adjusted in a number of ways. For instance a higherloading of the drug will be associated with increased initial releaserates. By selecting particular ingredients and by controlling therelative amounts thereof in the preparation it is possible to adjust therelease profile of O-desmethyltramadol and in embodiments that providefor tramadol in a sustained release form, also the release profile oftramadol. Such particular ingredients for example are the matrixmaterials mentioned above, e.g., the polymeric materials mentionedabove.

Sustained Release from a Reservoir.

In further embodiments, the sustained release form comprises a reservoircontaining the active ingredient or active ingredients, or a pluralityof reservoirs each containing one or more active ingredients. Reservoirdevices usually consist of a semi-permeable barrier that is involved inthe release of the active ingredient from a central site within thetablet. The manufacturing process may involve incorporating laser-boredorifices in the semi-permeable membrane. Representative sustainedrelease forms comprising a reservoir are disclosed in for example U.S.Pat. No. 6,245,357. Other sustained release forms comprising a reservoirinclude for example an osmotic dosage form for delivering various drugsto a patient is presented in U.S. Pat. Nos. 3,845,770 and 3,916,899. Thedosage forms disclosed in these patents are manufactured, for example,comprising a wall that surrounds a compartment comprising a drug with anexit in the wall for delivering the drug to a patient. In U.S. Pat. Nos.4,008,719, 4,014,334, 4,058,122, 4,116,241 and 4,160,452 are madeavailable dosage forms comprising an inside and an outside wall made ofpoly(cellulose acylate) for delivering a dosage of drug to a patient inneed thereof.

Sustained Release from Bead and Multi-Particulates.

In further embodiments, the sustained release form comprises sphericalpellets containing the active ingredient and a spheronizing agent. Thesame active ingredient may also be blended in a plurality of sustainedrelease forms so as to provide a blend of spherical pellets withdiffering dissolution rates for extended release or pulsitile release.The pellets may be film-coated or not. The spheronizing agent may be anysuitable pharmaceutically acceptable material, which can be spheronizedtogether with the active ingredient to form pellets. The term ‘sphericalpellet’ is meant to comprise pellets, beads or spheroids that are moreor less of regular shape. In particular embodiments the shape is roundor about round, i.e., having or approaching the shape of a small sphere.

The average size of the pellets may vary but preferably the diameter isin the range of about 0.1 mm to 3 mm, in particular from about 0.5 mm toabout 2 mm, more preferably about 1 mm.

The size distribution of the pellets may vary but in general it ispreferred that it has limited variation. It may vary between within arange of 10 to 20%. The size distribution may vary in a statisticalmanner, i.e., in a bell-shaped curve wherein e.g., 90% or e.g., 95% ofthe number of pellets are within a size range that varies between about10% to about 20% of the average sizes mentioned above.

The active ingredient (i.e., O-desmethyltramadol and optionally furthertramadol) or its pharmaceutically acceptable salt is present in anamount, which is in the range of from about 0.1 to about 50%, inparticular from about 1 to about 40%, more in particular from about 10to about 35%, w/w relative to the total weight of the pellet.

The pellets may further comprise an appropriate carrier which may be anycarrier known in the art used for making pellets. Particular carriermaterials are spheronizing agents that may be any suitablepharmaceutically acceptable material, which may be spheronized togetherwith the active ingredient to form pellets. A preferred spheronizingagent is microcrystalline cellulose. The microcrystalline cellulose usedmay suitably be, for example, the product sold under the trade name‘AVICEL™’. The spheronizing agent is present in an amount, which is inthe range of from about 25% to about 90%, in particular from about 35%to about 70% w/w, relative to the total weight of the pellet.

Optionally the pellets may contain other pharmaceutically acceptableingredients such as binders, bulking agents and colorants. Suitablebinders, some of which may also contribute to the sustained releaseproperties of the pellets, include water-soluble polymers, e.g.,water-soluble hydroxyalkyl celluloses such as hydroxypropyl celluloseand hydroxypropylmethyl cellulose, or water insoluble polymers, such asacrylic polymers or copolymers, or alkyl celluloses such as, forexample, ethylcellulose. Suitable bulking agents include lactose orcolloidal silicon dioxide. The amount of these other ingredients in thepellets will be relatively small, e.g., lower than 30%, or 20%, or evenlower than 10% or 5% w/w relative to the total weight of the pellet.

The pellets for use in the preparations of some embodiments are made byan extrusion process followed by spheronization. The mixture used in theextrusion process comprises active ingredient, a suitable carriermaterial and other optional ingredients, and a suitable lubricant. Thelubricant usually is water and the mixture for extrusion typically isconverted into a granulate. After extrusion, the extrudate isspheronized to obtain pellets. If desired, the latter may be coated witha suitable coating material.

If the active ingredients act as an additional binder in the mixturethat is extruded and spheronized (i.e., form a sticky mass upon contactwith water and/or the other excipients used in the extrudate mixture),the addition of a dry lubricant will be preferable. Apart from providinglubrication, the dry lubricant also allows the material to be extrudedat a much lower moisture content thereby reducing the sticking observedin the spheronizer.

Further embodiments thus are spherical pellets for sustained releasecomprising O-desmethyltramadol or tramadol or a salt thereof, or0-desmethyltramadol and tramadol or salts thereof, a spheronizing agentand dry lubricant. In a further aspect, said pellets have a low watercontent. If desired, the pellets may be coated.

The dry lubricant in particular is a mono-, di- or triglyceride, ormixtures thereof. Suitable mono-, di- or triglycerides are the mono-,di- or triesters of glycerin and one or more fatty acids. The mono-, di-or triglycerides may contain the same or different fatty acid residuesor mixtures thereof, e.g., technical mixtures obtained fromsaponification of natural oils. Of particular interest are fatty acidtriglycerides wherein the fatty acid residue has from 12 to 30 carbonatoms and is saturated or partially unsaturated or may be substituted,e.g., with one or more hydroxy functions. Preferred are mono-, di- ortriglycerides derived from C₁₈₋₃₀ fatty acids, in particular derivedfrom C₂₂₋₂₆ fatty acids. Of particularly preferred interest are behenicacid mono-, di- or triglycerides.

The dry lubricant preferably is solid at room temperature and has amelting point or melting range which is in the range of 60° C. to 90°C., in particular is in the range of 70° C. to 80° C. A particularlysuitable dry lubricant is the glyceride mixture sold under the tradename ‘COMPRITOL™ 888ATO’ which is a mixture of glyceryl mono-, di- andtribehenate, the dibehenate fraction being predominant, and having amelting range of about 69-74° C.

Preferably, the dry lubricant is selected such that it does not impactthe dissolution behavior of the active ingredient.

The dry lubricant is present in an amount, which is in the range of fromabout 2% to about 50%, in particular between 10% and 35% w/w, relativeto the total weight of the pellet.

Of particular interest are pellets that have a low water content. Inparticular embodiments, the water contents in the pellets is lower than5%, more in particular lower than 3%, w/w relative to the total weightof the pellet.

The spherical pellets, containing a dry lubricant, can be prepared by aprocess comprising extruding a mixture of the active ingredient with asuitable carrier in the presence of a dry lubricant and spheronizing theextrudate, wherein the dry lubricant is a triglyceride. The amount ofdry lubricant in this mixture may vary but in general is comprisedbetween 10% and 35% (w/w). A small amount of water may be added to themixture. In a particular execution, the amount of water is 5% or lower,or 3% or lower, or 1.5% or lower, w/w, relative to the total weight ofthe mixture for extrusion. In a specific process the pellets aresubsequently coated with a suitable coating.

The ingredients may be mixed together in any given sequence. In oneembodiment, the dry lubricant is added to a mixture of active ingredientand the carrier material at room temperature. The mixture issubsequently extruded through a small orifice. The diameter of thelatter is in relation to the size of the pellets that are eventuallyproduced from the extrudate. In one embodiment, the diameter of theorifices is in the range of 0.5 mm to 2.0 mm. The extrusion may be doneat slightly elevated temperature but preferably is performed withoutapplied heating. The extrudated material is subsequently placed into aspheronizer where it is spun at high speed.

In specific embodiments of this disclosure, the pellets (or spheroids),with or without dry lubricant, are subsequently coated with a suitablecoating using art known methods. The coating can either be a functionalcoating or a diffusion controlling coating.

A functional coating may be applied for e.g., taste masking, protectionof the pellets, to have improved stability (shelf-life) or foridentification (for example by coloring). Functional coating often willbe film coating, using any film coating material conventional in thepharmaceutical art. Preferably an aqueous film coating is used.

Diffusion controlling coatings are designed to achieve a target releaseprofile such as controlled or sustained release permitting release ofthe active ingredient at a controlled rate in an aqueous medium.Suitable controlled or sustained release coating materials includewater-insoluble waxes and polymers such as polymethacrylates, forexample EUDRAGIT™ polymers, or water insoluble celluloses, in particularalkyl celluloses such as ethylcellulose. Optionally, water-solublepolymers such as polyvinylpyrrolidone or water-soluble celluloses suchas hydroxypropylmethyl cellulose (HPMC) or hydroxypropylcellulose (HPC)may be included. Further components that may be added are water-solubleagents such as polysorbate. Of particular interest is ethylcellulose(EC). Preferably, a suitable plasticizer is added. A coating materialthat is particularly suitable is the coating material sold under thetrade name SURELEASE™ (Colorcon), which is a dispersion ofethylcellulose.

Alternatively the active ingredient or its salt-form may be coated ontoinert non-pareil beads, in particular onto sugar beads, and the drugloaded beads coated with a material, which permits control of therelease of the active ingredient into the aqueous medium.

Because of the bitter taste of one or more of the active ingredients,the pellets may be coated for taste-masking purposes although this maybe of less importance if the pellets are used in a capsule dosage form.

Placement of Active Ingredients in the Dose Form.

The tramadol in the preparations can be present throughout thepharmaceutical preparations disclosed herein, or in particular sectionsthereof. In particular embodiments it is present in one or more phasesof the preparations. Preferably, the tramadol is present in one or morephases that do not contain M1.

The phases can take a variety of forms, e.g., sections in a tablet, orthey can take the form of pellets. These forms can be prepared followingart-known procedures. In the particular case of sections in a tabletpreparation, procedures can be applied such as granulation followed bypartial or complete compression, or direct partial or completecompression.

Usually, the tramadol is formulated into a suitable formulation. This isprepared by mixing tramadol with suitable ingredients into differentformulation types such as powders, granulates, pellets and the like. Thepowder or granulate formulations may be compressed partially orcompletely to form appropriate phases for incorporation in bi- ormulti-phasic preparations. Particular phases are layers forincorporation in bi- or multi-layer tablets. Most preferably, thetramadol formulation will be for immediate release, i.e., theingredients and the formulation form are selected such that release oftramadol is as quickly and as complete as possible. Ideally, release is100% after a short period of time, e.g., within ½ hour.

In tablet preparations, suitable tableting excipients may be added e.g.,one or more of the standard excipients such as diluents, lubricants,binding agents, flow aids, disintegrating agents, surface active agentsor water soluble polymeric materials. Suitable diluents are e.g.,microcrystalline cellulose, lactose and dicalcium phosphate. Suitablelubricants are e.g., magnesium stearate and sodium stearyl fumarate.Suitable binding agents are e.g., hydroxypropyl methyl cellulose,polyvidone and methyl cellulose. Suitable disintegrating agents arestarch, sodium starch glycolate, crospovidone and croscarmellose sodium.Suitable surface active agents are POLOXAMER 188®, Polysorbate 80 andsodium lauryl sulfate. Suitable flow aids are talc, colloidal anhydroussilica.

Double Layer Tablets.

One particular execution of the sustained release preparations of thepresent disclosure are double layer (or bilayer) tablets. These compriseone layer containing M1 dispersed in a suitable matrix and another layerthat contains tramadol.

The tramadol containing layer preferably is composed of excipientstypically used for tramadol oral dosage forms such as tablets. Examplesof such excipients comprise any of those mentioned above in relation tothe immediate-release formulation of tramadol.

The M1 layer comprises any of the sustained release matrix materialsdescribed above. The matrix may in particular comprise polyvinyl acetateand polyvinylpyrrolidone and mixtures thereof, more in particular themixture known as KOLLIDON® SR. Or alternatively, the M1 layer maycomprise a hydrophilic swellable polymeric matrix such ashydroxypropylmethyl cellulose and a salt (i.e., an ‘electrolyte’) asdescribed more fully in U.S. Pat. No. 6,090,411.

The M1 layer may contain from about 10 mg to 100 mg M1 hydrochloride perunit, preferably from about 15 mg to about 75 mg of M1 hydrochloride perunit, or from about 20 mg to about 40 mg of M1 hydrochloride per unit.In case of application of M1-free base or other salts, an equivalentamount of active on a molar basis is used.

In particular embodiments, the M1 layer contains an effective amount ofM1, or a pharmaceutically acceptable salt thereof, dispersed in a matrixwherein the matrix contains from about 20% to about 90%, in particularfrom about 30% to about 80% of polyvinyl acetate andpolyvinylpyrrolidone, more in particular a mixture thereof, still morein particular the 8:2 (w/w) polyvinyl acetate:polyvinylpyrrolidonemixture known as KOLLIDON® SR. The percentages mentioned herein are w/wrelative to the total weight of the dosage form.

The M1 layer may additionally contain further ingredients such as theingredients mentioned previously in relation to the tramadol layer, inparticular starches, kaolin, lubricants, binders and the like. Preferredadditional carriers are lubricants, e.g., magnesium stearate, flowenhancers or fillers, e.g., silica (silicon dioxide), cellulose, fillerssuch as sugars, in particular lactose, titanium dioxide and the like.

In further particular embodiments, the M1 layer containsmicrocrystalline cellulose (MCC) as a filler and magnesium stearate as alubricant. MCC is added to improve compressibility of the blend.Magnesium stearate is added to avoid tablet sticking on the lower orupper punch during the compression. The concentration of magnesiumstearate in the M1 layer may vary but good results are obtained whenadding it in amounts ranging from about 0.5 to about 1.5% (w/w relativeto the total weight of the dosage form). The concentration of MCC in theM1 layer may vary but good results are obtained when adding it inamounts which range from about 5% to about 80%, preferably from about10% to about 65%, more preferably from about 20% to about 50% (w/wrelative to the total weight of the dosage form).

The M1 layer can be prepared by mixing M1 or its salt form withpolyvinyl acetate and polyvinylpyrrolidone, more in particular themixture thereof, still more in particular with KOLLIDON® SR while addingoptional ingredients. The latter may also be added after the mixing ofM1 and KOLLIDON® SR. The thus obtained mixtures are subsequentlycompressed, either by direct compression, which is preferred or bypreparing a granulate and subsequent compression.

It has been found that when using M1 and polyvinyl acetate andpolyvinylpyrrolidone mixtures, the tablets can be prepared by directcompression. The mixtures for direct compression preferably contain alubricant, in particular magnesium stearate. They may additionallycontain a filler, in particular a sugar such as lactose. They mayfurthermore contain a flow enhancer (i.e., a glidant) such as colloidalsilica (silicon dioxide). In the mixtures for direct compression thelubricant preferably is present in concentrations in the range of about0.5% to about 1.0%. The filler is present in concentrations from about5% to about 80%, preferably from about 10% to about 65%, more preferablyfrom about 20% to about 50%. The flow enhancer is present inconcentrations from about 0.4% to about 1.5%, preferably about 0.5% toabout 1.0%. All percentages herein are w/w relative to the total weightof the M1 containing phase or phases.

Particular embodiments are coated tablets, in particular film-coatedtablets. Coated tablets are easier to swallow than uncoated tabletcores, are usually easier to distinguish from other tablet, inparticular when the film-coat contains a dye or a pigment, and mayfurthermore have an improved stability (shelf-life). In the presentinstance coating is mainly for taste masking purposes because of thebitter taste of M1 and tramadol. Coatings are applied using art knownmethods using art known materials usually applied for this purpose.Particularly attractive coating products are based on suitablefilm-forming polymers such as hydroxypropylmethylcellulose (HPMC) orpolyvinylalcohol (PVA). Preferably, a plasticizer is added. Examples ofsuitable plasticizers are polyethylene glycol or derivatives thereofsuch as polyethoxylated alkylglycerides, e.g., polyethoxylated stearylmonoglyceride, in particular the material sold under the trade nameMacrogol. Further ingredients may be added to the coating such asfillers, dyes or pigments, flavors, sweeteners and the like components.Examples of such further ingredients are lactose, titanium dioxide,starch and the like. Particularly suited as coating materials are theOPADRY™ materials which mainly contain the before mentioned materialsand further ingredients such as plasticizers, e.g., polyethylene glycol.

In a preferred embodiment, first the M1 layer is produced by directcompression whereupon tramadol granules are placed on top of thecompressed M1 layer as to form a second layer whereupon the whole iscompressed to form a bi-layer tablet.

In particular embodiments there are provided bi-layer tablets comprisingan M1 layer and a tramadol layer wherein both layers are separated by asuitable layer that may function as an isolator. This third layer may becomprised of suitable inert materials such as cellulose or lactose. Suchembodiments may be prepared by first producing the M1 layer by partialor complete compression of a suitable M1 containing mixture whereuponthe isolator material is put on the M1 layer followed by a secondcompression, whereafter a suitable tramadol containing mixture is put ontop of the isolator layer as to form a third layer whereupon the wholeis compressed to form a tri-layer tablet. The suitable M1 containingmixture or suitable tramadol mixture may be a powder suitable for directcompression or a granulate obtained by a granulation process. Theisolator layer may be desirable e.g., to avoid certain interactionsbetween the components in each layer or to shield off humidity.

Multi-Layer Tablets.

Further embodiments are multi-layer tablets having multiple layers oftramadol and M1, optionally separated by one or more isolator layers.

Further Tablet Formulations.

In still further embodiments are M1 tablets coated with a tramadolcoating. In this type of preparations, a suitable core containing M1 ora salt thereof in a sustained release form is coated with atramadol-containing coating, e.g., by spraying with a suitable liquidformulation that contains tramadol. The core itself can be a tablet oranother shaped phase.

Still further embodiments are so-called “bull-eye” tablets, which aretablets with a cavity in which another tablet fits. The tablet with thecavity in particular is U-shaped.

The tablet with a cavity may contain the M1 and the other tablet thetramadol or vice versa. Bull-eye tablets can be made following art-knownprocedures using specially adapted punches in a tableting machine.

In any of the preparations that are tablets, the latter may be coatedwith a suitable coating material.

Preparations with Pellets.

Further embodiments are dosage forms comprising M1 formulated inpellets, hereafter referred to as ‘M1 pellets’. The M1 pellets may beprepared according to methods as described above and may be coated, ifdesired.

The M1 pellets in turn may be coated with a tramadol containing coating,e.g., by spraying the M1 pellets with an appropriate formulationcontaining tramadol. These M1 pellets with a tramadol coating may befilled into capsules.

The M1 pellets can be filled in capsules together with an appropriateformulation of tramadol e.g., formulated as a powder, granulate, orformulated itself as a pellet. The M1 pellets and the tramadolformulation may be filled into the capsule in any give sequence, firstthe M1 pellets followed by the tramadol formulation or vice versa or thetwo together or the two together as a mixture, e.g., a mixture oftramadol and M1 pellets.

In further embodiments there are provided capsules containing M1 pelletsand one or more tramadol tablets. The tramadol tablets will evidently beof such size and shape that it fits into a capsule. Preferably only onetramadol tablet is filled into one capsule.

In still further embodiments there is provided a so-called ‘capsule intocapsule’ dosage form, i.e., a capsule containing a suitable tramadolformulation is put into a bigger capsule containing M1 pellets. Or viceversa, a capsule containing M1 pellets is put into a bigger capsulecontaining a suitable tramadol formulation. A suitable tramadolformulation can be a powder or a pellet formulation.

Still other embodiments are sachets filled with amounts of M1 pelletsand a suitable tramadol formulation.

In still another aspect, an embodiment concerns a process formanufacturing a pharmaceutical dosage from, said method comprisingfilling the M1 pellets into a suitable container and further adding asuitable tramadol formulation. In a preferred aspect the container is acapsule. Another type of container is a sachet.

A particular embodiment provides unitary dosage forms which comprise M1HCl pellets as described herein in an amount that is such that thedosage form contains an effective amount of M1 HCl. Particularembodiments of such dosage forms may contain from about 10 mg to 100 mgM1 HCl per unit, preferably from about 15 mg to about 75 mg of M1 HClper unit, or from about 20 mg to about 50 mg of M1 HCl per unit.

In general, the all the compositions above may be presented in unitdosage form. Preferred unit dosage formulations are those containing aneffective dose, or an appropriate fraction thereof, of the activeingredient, or a pharmaceutically acceptable salt thereof. The magnitudeof a prophylactic or therapeutic dose typically varies with the natureand severity of the condition to be treated and the route ofadministration. The dose, and perhaps the dose frequency, will also varyaccording to the age, body weight and response of the individualpatient.

In general, the total daily dose of M1 ranges from about 40 mg per dayto about 200 mg per day, preferably about 60 mg per day to about 160 mgper day, and more preferably, about 80 mg per day to about 160 mg perday, in single or divided doses. If given together with M1 in optionalembodiments, the total daily dose of tramadol ranges from about 20 mgper day to about 400 mg per day, preferably about 40 mg per day to about300 mg per day, and more preferably, about 60 mg per day to about 200 mgper day, in single or divided doses. It is further recommended thatchildren, patients over 65 years old, and those with impaired renal orhepatic function, initially receive low doses and that the dosage istitrated based on individual responses and blood levels. It may benecessary to use dosages outside these ranges in some cases, as will beapparent to those in the art. Further, it is noted that the clinician ortreating physician knows how and when to interrupt, adjust or terminatetherapy in conjunction with individual patient's response.

Tramadol is commercially available from a variety of sources, or may bemade by the process described in U.S. Pat. No. 3,652,589, which isincorporated by reference herein. O-desmethyltramadol may be synthesizedfrom tramadol by demethylation of tramadol according to methods in theart, using for example, DIBAL or Ph₂PH and an alkyl lithium compound(U.S. Pat. No. 6,780,891, the disclosure of which is incorporated byreference herein). Racemic O-desmethyltramadol may thus be obtained bydemethylation of racemic tramadol, which is commercially available as aracemic mixture of the (R,R)- and (S,S)-enantiomers. Racemic tramadolmay be resolved to yield its individual enantiomers and demethylatedaccordingly to yield the corresponding enantiomer of O-desmethyltramadol(U.S. Pat. No. 5,728,885, the disclosure of which is incorporated byreference herein). Thus, demethylation of (1R, 1S)-tramadol will yield(1R,2R)—O-desmethyltramadol, and demethylation of (1S,2S)-tramadol willyield (1S,2S)—O-desmethyltramadol.

The enantiomers of tramadol HCl may be resolved using a modification ofthe procedure described in U.S. Pat. No. 3,652,589, the disclosure ofwhich is incorporated by reference herein, using D- or L-dibenzoyltartaric acid (DBTA). Other methods that may be used for the resolutionof enantiomers include formation of diastereoisomeric salts or complexesor derivatives which may be separated, for example, by crystallization,gas-liquid or liquid chromatography; selective reaction of oneenantiomer with an enantiomer-specific reagent, for example, enzymaticoxidation or reduction, followed by separation of the modified andunmodified enantiomers; and gas-liquid or liquid chromatography in achiral environment, for example, on a chiral support, such as silicawith a bound chiral ligand or in the presence of a chiral solvent. Itwill be appreciated that where the desired enantiomer is converted intoanother chemical entity by one of the separation procedures describedabove, a further step is typically required to liberate the desiredenantiomeric form. Alternatively, specific enantiomer may be synthesizedby asymmetric synthesis using optically active reagents, substrates,catalysts or solvents, or by converting one enantiomer to the other byasymmetric transformation.

Part I. Active Pharmaceutical Ingredient Example 1 (+/−)-Tramadol FreeBase

Racemic tramadol hydrochloride (5.00 g, 16.7 mmol, Fluka) was dissolvedin H_(2O) (50 ml). 10 N NaOH (2 ml) was added dropwise at roomtemperature, and a cloudy emulsion formed. The mixture was stirred for15 minutes, then extracted into CH₂Cl₂. The combined organic filtrateswere pooled, and washed with saturated NaCl, then dried over Na₂SO₄. Thesolution was filtered, then evaporated to yield a clear oil (4.30 g,98%).

Example 2 (+/−)-O-Desmethyltramadol Free Base (M1)

Tramadol free base (50.3 g, 191 mmol) was dissolved in anhydrous toluene(130 mL) in an oven-dried 2 liter round bottom flask. The solution wascooled in an ice bath, and 1M diisobutylaluminum hydride (DIBAL) intoluene (500 mL, 500 mmol, 2.6 eq.) was added dropwise to the cooledsolution under a nitrogen atmosphere. The addition took place over aperiod of 4.5 hours. Following addition, the solution was kept in theice bath for 30 minutes, then allowed to warm to room temperature, thenrefluxed for 18 hours. The solution was removed from heat, and allowedto cool to room temperature, then placed in an ice bath. Anhydrousethanol (250 mL) was then added dropwise to the solution over a periodof 2 hours. Following addition, the solution was transferred to a 2liter beaker, and water (250 mL) was added with vigorous stirring. Thereaction mixture was filtered, and the toluene layer washed with water,saturated aqueous sodium chloride, and dried over sodium sulfate. Thesolution was filtered and evaporated to yield 38.1 grams of a whilesolid (80% yield). Analysis of this material by LC-MS in positive modeindicated that the material was >95% pure with the main peak having amass consistent with M1 (m/z=250). Elemental analysis: (theory) C,72.25; H, 9.30; N, 5.62, and 0, 12.83; (found) C, 72.43; H, 9.35; N,5.66; and 0, 12.79.

Example 3 (+/−)-O-Desmethyltramadol HCl (M1 HCl)

In a three necked flask equipped with a thermometer, M1 free base (33.5g, 135 mmol) was dissolved in anhydrous isopropyl alcohol (230 mL) andcooled in an ice bath. Anhydrous hydrogen chloride (g) was bubbled intothe solution slowly as to keep the reaction temperature below 25° C.After the introduction of >7 grams of HCl (>195 mmol), the reactionflask was stoppered, and removed from the ice bath. A white precipitateformed upon cessation of HCl. The reaction mixture was allowed to warmto room temperature over 30 minutes, then vacuum filtered with a Buchnerfunnel. The filtered material was washed with anhydrous isopropylalcohol, and dried under vacuum to constant weight to yield 33 grams ofa white solid (86%). Analysis of this material by LC-MS in positive modeindicated that the material was >98% pure having a mass consistent withM1 (m/z=250). Elemental analysis: (theory) C, 63.04; H, 8.46; N, 4.90;and 0, 11.20; (found) C, 63.13; H, 8.53; N, 4.90; and 0, 11.20.

Part II. Immediate Release Dosage Forms Example 4 LiquidImmediate-Release Oral Dosage Form

Racemic M1 was fully solubilized in water at a concentration of 1 mg/mlby adding 50 mg M1 HCl to 50 ml of water to provide Solution A. Theappropriate amount of M1 was provided to a human subject by dispensingthe appropriate volume of Solution A.

Example 5 Tablet Immediate-Release Oral Dosage Form

Table 1 provides the ingredients for an immediate-release tablet dosageform. The active ingredients are blended with the cellulose until auniform blend is formed. The smaller quantity of starch is blended witha suitable quantity of water to form a starch paste. This is then mixedwith the uniform blend until a uniform wet mass is formed. The remainingcornstarch is added to the resulting wet mass and mixed until uniformgranules are obtained. The granules are then screened through a suitablemilling machine, using a 14 inch stainless steel screen.

The milled granules are then dried in a suitable drying oven until thedesired moisture content is obtained. The dried granules are then milledthrough a suitable milling machine using¼ mesh stainless steel screen.The magnesium stearate is then blended and the resulting mixture iscompressed into tablets of desired shape, thickness, hardness anddisintegration. Tablets are coated by standard aqueous or nonaqueoustechnique. Tablets of other strengths may be prepared by altering theratio of active ingredients to pharmaceutically acceptable carrier, thecompression weight, or by using different punches.

TABLE 1 Quantity per Tablet (mg) Formula Formula Formula Formula FormulaComponent A B C D E Racemic O-desmethyl- 40 40 20 20 20 tramadol HClRacemic tramadol HCl 0 30 15 12.5 10.0 Microcrystalline 114.5 84.5 119.5122 124.5 cellulose NF Starch NF 30 30 30 30 30 Pregelatinized maize 1515 15 15 15 starch NF Magnesium stearate 0.5 0.5 0.5 0.5 0.5 CompressionWeight 200 200 200 200 200

Example 6 Human Single-Dose Pharmacokinetics of Immediate ReleaseTramadol and O-Desmethyltramadol

An 88 kg healthy male subject who met certain inclusion/exclusioncriteria was enrolled in an open-label pharmacokinetic study. Thesubject has a CYP2D6*1/*4 intermediate metabolizer genotype (+35% ofpopulation). He received a 100 mg oral dose of racemic tramadol HCl inthe form of a commercially available immediate-release tablet (i.e., two50 mg ULTRAM® tablets, the reference listed drug per FDA Orange Book),followed by escalating weekly oral doses of racemic O-desmethyltramadolHCl given as the liquid immediate-release oral dosage form (i.e.,Solution A from Example 4). In vitro dissolution data for the ULTRAM®tablets were obtained by us per the FDA CDER method database. In vitrodissolution of the immediate-release ULTRAM® tablets was 70% at 10 min,and 100% at 20 min.

All doses were separated by a 7 day washout period. In particular, afteran overnight fast, the subject received a single oral dose of 100 mgracemic tramadol HCl consisting of two 50 mg tablets of a commercialimmediate-release formulation with tap water. Seven days later, the samesubject received a single oral dose of 20 ml of 1 mg/mlO-desmethyltramadol HCl fully solubilized in water (i.e., Solution A, 20mg dose total), followed by the ingestion of additional tap water. Sevendays after that, the same subject received a single oral dose of 40 mlof 1 mg/ml O-desmethyltramadol HCl fully solubilized in water (i.e.,Solution A, 40 mg dose total), followed by the ingestion of additionaltap water. No food was allowed until 4 hours after administration.

For pharmacokinetic analysis, venous blood samples with EDTA asanticoagulant were taken before each dosing and at 0.5, 1, 1.5, 2, 3, 4,6, 8, 10, 12, and 24 hours after each dosing. Samples were centrifuged,and the plasma collected and stored frozen at −20° C. for analysis.There was no urine sampling in this study.

Tramadol and O-desmethyltramadol in plasma samples were quantitated byan LC/MS assay using an internal standard consisting of isotopicallylabeled tramadol (Cantest, Burnaby, British Columbia, Canada). Thequantitation range of the LC/MS assay was 1.00-500 ng/mL for bothtramadol and O-desmethyltramadol.

Noncompartmental methods of analysis were used to calculatepharmacokinetic parameters using PK Solutions Version 2.0. The method ofresiduals (i.e., curve stripping or feathering) was used to resolve theconcentration-time profile curve of parent or M1 into a series ofexponential terms corresponding to the absorption, distribution, andelimination phases occurring during the time course in the blood. Theseexponential terms were then used to calculate the single-dosepharmacokinetic parameters following well established formulae. Thesingle-dose pharmacokinetic data from this study are shown graphicallyfor plasma tramadol (FIG. 1A), and plasma M1 (FIG. 1B) and thesingle-dose pharmacokinetic parameters summarized in Table 2.

The single-dose pharmacokinetic parameters for this male subjectobtained for 100 mg tramadol agreed well with the mean single-dosepharmacokinetic parameters in the drug labeling (label data for parent:C_(max)=308 ng/mL; T_(max)=1.6 hr; half-life=5.6 hr; and label data forM1: C_(max)=55 ng/mL; T_(max)=3.0 hr; half-life=6.7 hr). However,compared with immediate-release tramadol, the half-life of plasma M1from immediate-release M1 was surprisingly very different, beingsignificantly reduced by about half. Without wishing to be limited bytheory, it is hypothesized that this is due to tramadol serving as acirculating slow-release depot for M1, where tramadol is a prodrug thatis metabolized in the liver slowly over time.

TABLE 2 Substance Dose Dosage AUC_((0-t)) AUC T_(max) C_(max) ClearanceHalf-Life Dosed (mg) (mg/kg) (hr-ng/mL) (hr-ng/mL) (hr) (ng/mL)(ml/hr/kg) (hr) Tramadol 100 1.14 2463* 2626* 2.0 274*  433* 5.9* HCl 812**  906** 3.0  66.8** 1255** 7.1** M1 HCl 20 0.23  351  357 2.0 52.3  638 4.1 M1 HCl 40 0.46  619  633 1.5  88.6  719 4.4 *The parent,tramadol. **The M1 metabolite, O-desmethyltramadol.

The human data for tramadol and its M1 metabolite in this exampledemonstrated, (i) efficient oral bioavailability of M1 in the human thatdoes not depend on tramadol metabolism, and (ii) a correlation betweenthe M1 AUC for an oral M1 dose vs. an oral tramadol dose (i.e., 40 mg ofM1 yielded an M1 AUC about 70% of that obtained from 100 mg tramadol).

Example 7 Human Steady-State Pharmacokinetics of Immediate ReleaseTramadol and 0-Desmethyltramadol

The same 88 kg healthy male subject in Example 6 was enrolled in anopen-label steady-state pharmacokinetic study. He received 10consecutive oral doses with water every 6 hours (sufficient to reachsteady-state) of either 25 mg, 50 mg, 75 mg or 100 mg racemic tramadolHCl in the form of a half, 1 whole, 1 whole and 1 half, or 2 wholetablets of the commercially available immediate-release tabletformulation (i.e., 50 mg ULTRAM®), respectively. In addition to thesefour ten-dose sequences, he also received a dosing sequence consistingof 10 doses every 6 hours of 20 mg racemic O-desmethyltramadol HCl givenas an immediate-release gelatin capsule containing 20 mgO-desmethyltramadol HCl powder (i.e., ‘20 mg M1 IR’). Each ten-dosesequence was separated by at least a 12 hour washout, although a washoutperiod was not strictly required in this study since steady-state isestablished by the 8^(th) dose, a time when there is effectively noremnant of the previous sequence. There were no food or fastingrestrictions.

For pharmacokinetic analysis, 23 venous blood samples (EDTA) were takenat 0.0, 0.25, 0.50, 0.75, 1.0, 1.25, 1.5, 2, 3, 4, 5 and 6 hours afterthe 9^(th) and 0.25, 0.50, 0.75, 1.0, 1.25, 1.5, 2, 3, 4, 5 and 6 hoursafter the 10^(th) doses (i.e., the 6 hour time point of the 9^(th) doseis equivalent to the 0.0 time point for the 10^(th) dose). Samples werecentrifuged, and the plasma collected and stored frozen at −20° C. foranalysis. There was no urine sampling in this study. Tramadol andO-desmethyltramadol in plasma samples were quantitated by an LC/MS assay(Warnex, Canada).

The steady-state pharmacokinetic data for the plasma M1 concentrationsfrom this study are shown graphically in FIG. 2A and FIG. 2B thesteady-state pharmacokinetic parameters for the plasma parent and for M1concentrations, as summarized in Table 3. The steady-statepharmacokinetic parameters for this male subject dosed with 100 mgracemic tramadol HCl agreed well with the mean steady-statepharmacokinetic parameters for the same dose in the drug labeling (labeldata for parent: C_(max)=592 ng/mL; T_(max)=2.3 hr; and label data forM1: C_(max)=110 ng/mL; T_(max)=2.4 hr).

TABLE 3 Dose 9 Dose 9 Dose 10 Dose 10 Mean* Mean* Mean* Dose Css_(min)Css_(max) Css_(min) Css_(max) Css_(min) Css_(max) ΔCss T_(max)*Substance^(†) (mg) (ng/mL) (ng/mL) (ng/mL) (ng/mL) (ng/mL) (ng/mL)(ng/mL) (hr) Plasma M1 Tramadol HCl 25 22 29 16 33 19 31 12 1.38Tramadol HCl 50 45 59 33 58 39 59 20 1.13 Tramadol HCl 75 64 91 53 81 5886 28 1.50 Tramadol HCl 100 88 114 58 113 73 114 41 1.50 M1 HCl 20 34 9434 108 34 101 67 1.25 Plasma Parent Tramadol HCl 25 53.6 101 50.5 137 52119 67 1.00 Tramadol HCl 50 136 269 141 294 139 282 143 1.13 TramadolHCl 75 198 368 193 438 196 403 208 1.38 Tramadol HCl 100 316 560 310 627313 594 281 1.13 M1 HCl 20 ND ND ND ND ND — — — ^(†)All inimmediate-release (IR) forms. *Mean of dose 9 and dose 10. ND = Notdetected. ΔCss = Css_(max) − Css_(min).

FIG. 2A shows the steady-state plasma M1 profile for the 20 mg M1 IRformulation vs. the predicted steady-state plasma M1 profile based onthe single-dose pharmacokinetic parameters for Solution A from Example6. FIG. 2B shows the steady-state plasma M1 profile for the 20 mg M1 IRformulation vs. the steady-state plasma M1 profile for the differentdoses of the commercially available immediate-release tramadol tablet(ULTRAM® tablets).

Compared to ULTRAM® tablets, the steady-state plasma profile for 20 mgIR M1 revealed a large difference in the mean steady-state maximum(Css_(max)) and mean steady-state minimum (Css_(min)) plasma M1concentrations (i.e., ΔCss) during dose cycles 9 and 10 (i.e., 67 ng/mL)that exceeded the corresponding value for even the largest dose ofULTRAM® (i.e., ΔCss=41 ng/mL). Furthermore, the values for Css_(max) andCss_(min) traversed and undershot the M1 therapeutic window provided byULTRAM® dosing per label (i.e., 50 to 100 mg q 6 hrs). Thus, both thesingle-dose and steady-state plasma M1 profiles for M1 administered asan immediate-release formulation were surprisingly very different thanthe plasma M1 profiles provided by therapeutically effective doses ofracemic tramadol HCl administered as an immediate-release formulation(i.e., ULTRAM® tablets). Again, without wishing to be limited by theory,it is hypothesized that when M1 is administered directly as an immediaterelease formulation it is rapidly cleared by liver metabolism and renalexcretion. In contrast, when tramadol is administered as an immediaterelease formulation, it serves as the molecular equivalent of acirculating slow-release depot for M1, prolonging the release of M1 andthus dampening the difference between Css_(max) and Css_(min) plasma M1concentrations during dose cycles.

FIG. 3 shows the mean steady-state M1 plasma concentration during doses9 and 10 as a function of the dose of racemic tramadol HCl administeredas an immediate-release formulation (i.e., ULTRAM® tablets). There wasexcellent linear dose proportionality for mean plasma M1 as a functionof tramadol dose (mean M1=0.95.times. dose, R²=0.9975).

Part III. Sustained-Release Dosage Forms Example 8 Sustained ReleaseOral Dosage Forms IIIa

A series of monolithic sustained release (SR) formulations based on CDT®technology as described in U.S. Pat. No. 6,090,411 were developed.

Manufacturing.

M1.HCl SR tablets were prepared through dry-blend and directcompression. The raw materials minus the lubricant were screened througha 30 mesh sieve and charged in a V-blender (Patterson-Kelly/HarscoCorporation. East Stroudsburg, Pa.) for 10 minutes of blending. Thelubricant was then screened through a 30 mesh sieve and added to the mixfor an additional 3 minutes of blending time. Batch formulae aredepicted in Table 4.

TABLE 4 Formulation (mg/tablet) SR Dosage Forms Raw Material PurposeManufacturer SR100 SR101 SR102 SR103 SR104 SR105 M1 HCl API In-House20.0 20.0 20.0 40.0 40.0 40.0 HPMC K4M Polymer Colorcon 25.0 25.0 50.025.0 50.0 100.0 Na Citrate Electrolyte Gadot 12.5 12.5 — 25.0 25.0 — NaBicarbonate Electrolyte Natrium — — 25.0 — — 50.0 AVICEL ® Flow AgentFMC 50.0 75.0 50.0 100.0 150.0 100.0 PH 102 MCC Mg Stearate LubricantMallinckrodt 1.5 1.5 1.5 3.0 3.0 3.0 Total mg/tablet 109.0 134.0 146.5193.0 268.0 293.0 Compression Pre-compression (KN) 0 0 0 0 0 0 Maincompression (KN) 10 10 10 10 17 12 Full travel ejection (N) 80 80 80 8080 80 Take-off (N) 1 1 1 1 1 1 Turret speed (rpm) 10 10 45 45 45 40Tooling A A A A B C Punch and die codes (Natoli Engineering): A =0.2812″ (HOB 91270); B = 0.2347″ × 0.5501″ (HOB 67146); C = 0.2812″ ×0.5000″ (HOB 58651). HPMC = hydroxypropylmethyl cellulose; MCC =microcrystalline cellulose.

The blend was charged to the hopper of a Piccola (Riva) 10-stationrotary press (Specialty Measurements Inc. Lebanon, N.J.). The rotarypress was fitted with the appropriate punch and die tooling andinstrumented with main compression, pre-compression, ejection, take-offand turret speed sensors. Settings for each batch are summarized inTable 4.

Tablet Characterization. The mean physical characteristics: weight,thickness, hardness and friability were tested along with in vitrodissolution testing in various physiological relevant media of pH 1.2,4.5 and 7.2 (Table 5). Dissolution of each SR formulation was determinedwith six tablets per formulation using a USP Type I dissolution assembly(VanKel VK-7000, Cary, N.C.) with a paddle speed of 75.+−0.0.1 rpm andbath temperature of 37.0.+−0.0.5° C. The dissolution medium was 900 mLof 0.1N HCl; pH 1.2, 0.05M acetate buffer; pH 4.5 or 0.05M phosphatebuffer; pH 7.2 (6 replicates per pH). Samples were detected on-line eachhour throughout the duration of release using a UV/vis spectrophotometerat 270 nm (Varian Cary 50, Cary, N.C.). Maximum absorbance values aftera 1 hour infinity spin were used to calculate release.

TABLE 5 SR Dosage Forms Characterization SR100 SR101 SR102 SR103 SR104SR105 *Weight (mg) 115.4 137.7 151.7 194.0 280.0 300.9 *Thickness (inch)0.120 0.132 0.134 0.175 0.158 0.175 *Hardness (kp) 7.6 11.5 10.1 10.113.8 13.9 *Friability (% loss) 0.28% 0.09% 0.05% 0.07% 0.13% 0.20%**Dissolution In Vitro Hrs to release 25% 0.29 0.34 0.53 0.34 0.45 1.0Hrs to release 50% 1.0 1.4 2.2 1.1 1.7 3.0 Hrs to release 75% 2.0 3.14.7 2.3 3.9 7.0 Hrs to release >90% 3.0 5.1 7.4 3.2 5.7 12.0 *Mean.**The hours (‘Hrs’) to the indicated % dissolution in vitro weredetermined from an equation (power or polynomial) fitted (R² > 0.99 forall) to the mean dissolution data for all media (i.e. pH 1.2, 4.5 and7.2).

The dissolution kinetics of formulations SR100 to SR105 weresubstantially independent of pH, with data from SR100 shown in FIG. 4 asbeing representative. In vitro dissolution kinetics that are independentof pH is considered evidence that in vivo dissolution kinetics willlikewise be independent of pH, and thus unaffected by variations ingastrointestinal motility and pH. This is considered a desirableproperty for an SR tablet that improves consistency of in vivo releasekinetics from subject-to-subject and from dose-to-dose in the samesubject.

The dissolution data of formulations SR100, SR101 and SR102 are depictedin FIG. 5A, with select data from testing presented in Table 5. Thedissolution data of formulations SR103, SR104 and SR105 are depicted inFIG. 5B, with select data from testing presented in Table 5. As shown inthe inset to FIG. 5B, plots of the fraction M1 released as a function ofthe square root of time (t charts) reveal linear correlations (R²>0.99)consistent with these formulations conforming to Higuchi releasekinetics (Higuchi T. ‘Mechanism of sustained action medication:theoretical analysis of rate of release of solid drugs dispersed insolid matrices’ J Pharm Sci. 1963; 52:1145-1149).

The SR100 to SR102 series was designed to substantially replicate athalf the M1 HCl dose (i.e., 20 mg vs. 40 mg M1 HCl) the dissolutionkinetics of the SR103 to SR105 series, respectively. FIGS. 6A-6C showthe direct comparisons of each SR form at 20 mg and 40 mg dose strength,confirms that the dissolution kinetics of SR100 is similar to that ofSR103, and SR101 is similar to that of SR104, and SR102 is similar (butless so than the other two pairs) to that of SR105.

Example 9 Sustained Release Oral Dosage Forms IIIb

A series of sustained release (SR) formulations comprising uncoated andcoated hydrophilic polymer cores were developed. Except for SR311, thatdelivered a 20 mg M1 HCl dose, all others in this section delivered a 40mg HCl dose or the molar equivalent of the M1 free base.

Materials.

All materials utilized for the preparation of tablets werepharmaceutical grade.

Active pharmaceutical ingredients (API) M1 (i.e., the free base) and M1HCl were obtained in house using syntheses described above. Tramadol HClextended release tablets (i.e., ULTRAM ER®) were procured from ParPharmaceuticals (Woodcliff, N.J.) and used as a control.

Tablet Manufacture.

Table 6, Table 7 and Table 8 list the excipient sources and compositionsof M1 and M1 HCl tablets prepared. Except for formulation SR311, allpowders were ground and screened through a 325 m mesh screen.Formulations were prepared in 3-5 g batches. Powders for eachformulation were premixed in a V-blender for 30 min. A 7 mm biconvextooling and die set was used for compression of the powders. Eachbiconvex tablet was individually compressed on a Carver press (Model C,Fred S. Carver Press, Menomonee Falls Wis.) at 5000±100 lbs of force anda dwell time of 30 sec for tablets containing HPMC K4M Premium CR and at3000+100 lbs of force and a dwell time of 30 sec for tablets containingKOLLIDON® SR. All tablets were allowed to stand at room temperatureovernight in a sealed scintillation vial to allow for any elasticrecovery.

Formulation SR311 was prepared through dry-blend and direct compression.The raw materials minus the lubricant were screened through a 30 meshsieve and charged in a V-blender (Patterson-Kelly/Harsco Corporation.East Stroudsburg, Pa.) for 10 minutes of blending. The lubricant wasthen screened through a 30 mesh sieve and added to the mix for anadditional 3 minutes of blending time. The blend was charged to thehopper of a Piccola 10-station rotary press (Specialty Measurements Inc.Lebanon, N.J.). Due to the extremely small amount of blend, the blendwas manually fed into the die to reduce waste of material. The toolingused was a round shaped, stainless steel punch and die with a 0.1875″diameter from Elizabeth Carbide. The rotary press was instrumented withmain compression, pre-compression, ejection, take-off and turret speedsensors. Pre compression was set to zero, main compression was measuredto be ±1.2 KN (maximum compression for tooling is 3.94 KN), full travelejection was measured at ±80N, take-off averaged ±1N and the turretspeed ran at 10 rpm.

TABLE 6 Formulation (% w/w) SR Dosage Forms Raw Material PurposeManufacturer SR201 SR202 SR203 SR204 SR205 SR206 M1 (free base) APIIn-House 39.02 39.02 39.02 39.02 39.02 — M1 HCl API In-House — — — — —39.02 AVICEL ® Binder/Filler FMC 48.79 39.04 29.26 19.53 9.77 19.53 MCCPH 101 HPMC K4M Hydrogel Dow 9.76 19.51 29.29 39.02 48.78 39.02Colloidal Silica Glidant Cabot 1.46 1.46 1.46 1.46 1.46 1.46 Mg StearateLubricant Mallinckrodt 0.97 0.97 0.97 0.97 0.97 0.97 Total % 100 100 100100 100 100 Tablet (mg) 102.5 102.5 102.5 102.5 102.5 102.5 HPMC =hydroxypropylmethyl cellulose; MCC = microcrystalline cellulose.

Tablet Coating.

Where indicated in Table 7, tablets were coated on a pilot scale pancoater (Bolden, Chicago, Ill.). The rotation speed was set to 60 rpm. AWheaton bench top glass atomizer/sprayer was placed 30 cm from the bedof the coating pan with a constant flow rate of 10 ml/min. The coatingsolution was prepared by dissolving the polymer, plasticizer and/or poreformer in acetone. Coating was performed until the desired gain intablet weight was achieved. A heat gun that had been set at 45° C. wasemployed for drying the coating solution after application on thetablets. The coated tablets were placed in an oven at 45° C. for 1 hrand then allowed to stand overnight at room temperature.

TABLE 7 Formulation (% w/w) SR Dosage Forms Raw Material PurposeManufacturer SR301 SR302 SR303 SR304 SR305 SR306 M1 HCl API In-House39.02 39.02 39.02 39.02 39.02 39.02 AVICEL MCC PH 101 Binder/Filler FMC39.02 39.02 39.02 39.02 39.02 39.02 HPMC K4M Hydrogel Dow 19.51 19.5119.51 19.51 19.51 19.51 Colloidal Silica Glidant Cabot 1.46 1.46 1.461.46 1.46 1.46 Mg Stearate Lubricant Mallinckrodt 0.97 0.97 0.97 0.970.97 0.97 Total % 100 100 100 100 100 100 Uncoated (mg) 102.5 102.5102.5 102.5 102.5 102.5 Coating Acetone* Solvent Fisher — 500 500 500500 500 Ethylcellulose** Film Former Dow — 99 95 90 85 89 PVP K-25**Pore Former ISP — 10 Dibutyl Sebacate** Plasticizer Kodak — 1 TriethylCitrate** Plasticizer/Pore Morflex — 1 5 10 15 Coated (mg) — 113.0 112.8112.9 112.9 107.6 HPMC = hydroxypropylmethyl cellulose; MCC =microcrystalline cellulose; PVP = poly(vinyl pyrrolidone). *mL, **% w/w.

Dissolution Testing Methodology.

Except for formulation SR31 1, the in vitro release profiles of M1 andM1.HCl from the tablets were examined in pH 1.2 and/or 7.4 buffersolution(s) (900 ml) at 37° C. and 50 rpm using a Hansen's six-stationUSP Type II paddle dissolution assembly (model SR-8, Hansen ResearchCorp., CA). The buffer solutions were prepared according to the USP31/NF 26 procedures (United States Pharmacopeia 31/National Formulary,Vol. 1, p. 813, Washington, D.C.). Aliquots (1 ml each) were withdrawnat predetermined time intervals and immediately replaced with an equalvolume of the fresh dissolution medium. The removed sample was dilutedwith 1 ml of 0.1N HCl and analyzed by high performance liquidchromatography (HPLC) (vide infra). All dissolution tests were performedin triplicate.

TABLE 8 Formulation (% w/w) SR Dosage Forms Raw Material PurposeManufacturer SR307 SR308 SR309 SR310 SR311 M1 HCl API In-House 33.3336.36 40.00 44.44 32.83 KOLLIDON ® Matrix Former BASF 66.66 63.63 60.0055.56 65.68 SR Colloidal Silica Glidant Cabot — — — — 0.99 Mg StearateLubricant Mallinckrodt — — — — 0.49 Total % 100 100 100 100 100 Tablet(mg) 120 110 100 90 60.90 HPMC = hydroxypropylmethyl cellulose; MCC =microcrystalline cellulose; KOLLIDON ® SR = polyvinyl acetate (8 partsw/w) and polyvinylpyrrolidone (2 parts w/w).

HPLC Methodology.

A fully automated Shimadzu SCL-10 chromatographic system, equipped witha Cis analytical column (Phenomenex Gemini, 150×3 mm, 110 degrees,particle size 3 μm) was employed. The drug was eluted with a 3:1 (v/v)mixture of water:methanol containing 2% acetic acid and 1%triethylamine. The flow rate was 0.2 ml/min, and the detector was set at274, 272 or 271 nm for tramadol HCl, M1 HCl and M1 free base,respectively. The drug content in the sample was determined by theabsolute calibration curve method.

SR311 Dissolution Testing Methodology.

Dissolution of SR311 was determined with six tablets per formulationusing a USP Type I dissolution assembly (VanKel VK-7000, Cary N.C.) witha paddle speed of 75+0.1 rpm and bath temperature of 37.0+0.5° C. Thedissolution medium was 900 mL of 0.1N HCl, pH 1.2; 0.05M acetate buffer;pH 4.5 or 0.05M phosphate buffer, pH 7.2 (6 replicates per pH). Sampleswere detected on-line each hour throughout the duration of release usinga UV/vis spectrophotometer at 270 nm (Varian Cary 50). Maximumabsorbance values after a 1 hour infinity spin were used to calculaterelease.

Results 1—Uncoated Monolithic HPMC-Based Tablets.

Monolithic HPMC-based tablets were prepared as formulations SR201 toSR206, and data from in vitro dissolution testing in physiologicalrelevant medium of pH 7.4 are shown in Table 9 for SR201 to SR205.Without being limited by theory, it is speculated that the releasemechanism for SR201 to SR206 involves (i) the hydration of the tabletand formation of a hydrogel matrix, and (ii) solubilization andsubsequent diffusion of the API through the hydrogel matrix. Thus, thehigher the HPMC K4M amount, the greater the diffusion barrier andconsequently, the slower the drug release. The dissolution kinetics offormulations SR201 to SR205 were dependent on pH, with data from SR204in media at pH 1.2 and 7.4 being representative. Without wishing to belimited by theory, it was hypothesized that the relative insolubility ofthe M1 free base makes the dissolution of these formulations highly pHdependent due to pH influencing the rate of conversion to the moresoluble M1 HCl salt. The development of SR206 that employed the M1 HClsalt, but otherwise had the same formulation as SR204, was intended tomake SR206 dissolution pH independent (dissolution kinetics for SR206herein are those of SR204 at pH 7.4). Consistent with this notion, therelease profile of M1 HCl from another uncoated HPMC K4M-based tabletSR301 was relatively pH independent, with data in media at pH 1.2 and7.4 shown in FIG. 7. The tramadol HCl extended release (ULTRAM ER®)control is shown for comparison. The advantages of SR tablet dissolutionthat is pH independent in terms of consistency of in vivo releasekinetics from subject-to-subject, and from dose-to-dose in the samesubject have been discussed above.

TABLE 9 Hours to Release Indicated Percent of API* Dissolution MediumHaving pH = 7.4 pH Independent 25% 50% 75% >90% Dissolution SR201 <0.02<0.02 0.11 1.7 No SR202 <0.02 <0.02 0.33 3.7 No SR203 <0.02 0.30 1.9 7.0No SR204 0.36 1.8 4.7 9.2 No SR205 3.5 8.3 13.8 19.8 No SR307 0.24 1.96.0 14 Yes SR308 0.14 1.0 3.5 8.0 Yes SR309 0.10 0.72 2.3 5.2 Yes SR3100.04 0.38 1.5 3.7 Yes SR311 0.23 1.0 3.5 7.5 Yes *The hours to theindicated % dissolution in vitro were determined from an equation (poweror polynomial) fitted (R² > 0.99 for all) to the mean dissolution datafor the indicated dissolution medium.

Results 2—Coated Tablets.

To further prolong the profile of SR301, coated formulations SR302 toSR305 were developed that had the same tablet core, but were now coatedwith ethylcellulose containing 1, 5, 10 and 15% of triethyl citrate as aplasticizer. As shown in FIG. 8, these formulations provided sustainedrelease profiles of longer duration than the Tramadol HCl ER (ULTRAMER®) control, and consistent with the pH independence seen previouslyfor the same uncoated SR301 core, were pH independent in their coatedform with data from SR302 in FIG. 9 being representative.

With the addition of the pore-forming agent PVP K-25 and thesubstitution of dibutyl sebacate for triethyl citrate as the plasticizerin the coating, the sustained release profile of SR306 shortened andsubstantially replicated that of the Tramadol HCl ER (ULTRAM ER®)control as shown in FIG. 10 (note that SR306 contains a different APIthan the ULTRAM ER® control). It is known that (i) coated sustainedrelease tablet formulations can be defeated by drug abusers throughsimple crushing of the tablet, and (ii) maintaining control overdissolution characteristics during commercial manufacturing can bechallenging. Accordingly, uncoated monolithic sustained release tabletsare generally more preferred over coated sustained release tablets.

Results 3—Uncoated Monolithic KOLLIDON® Based Tablets.

Monolithic KOLLIDON® based tablets were prepared as formulations SR307to SR311, and data from in vitro dissolution testing in physiologicalrelevant medium of pH 7.4 are shown in Table 9, and the release profilesshown in FIG. 11. In all cases, an initial burst release, followed by aslow release of M1 was observed. The dissolution of the KOLLIDON® basedtablets was independent of pH, as shown for SR311 in FIG. 12 as beingrepresentative.

Example 10 Human Single-Dose Pharmacokinetics of Sustained ReleaseO-Desmethyltramadol

The same 88 kg healthy male subject in Example 6 was enrolled in anopen-label single-dose pharmacokinetic study (genotype: CYP2D6*1/*4intermediate metabolizer, +35% of population). The subject received asingle oral dose of each of 12 different (i) SR formulations and (ii)SR+IR combination formulations having a variety of in vitro dissolutionkinetics, as summarized in Table 10. Data for single-dosings of IRcontrols Tramadol HCl (T₁=100 mg) and M1 HCl (M₁=20 mg, M₂=40 mg)formulations are reproduced from Table 2 for comparison purposes. Inaddition, the subject received a second single-dosing of the IR TramadolHCl (T₂=100 mg) control.

All doses were separated by at least a one day washout. Food was limitedfor 30 minutes before and after a dose, but was otherwise notrestricted. For pharmacokinetic analysis, venous blood samples with EDTAas anticoagulant were taken before each dosing and over 24 hours aftereach dosing (typically 14-16 samples). Samples were centrifuged, and theplasma collected and stored frozen at −20° C. for analysis. There was nourine sampling in this study. Tramadol and O-desmethyltramadol in plasmasamples were quantitated by an LC/MS assay (Warnex, Canada).

Noncompartmental methods of analysis were used to calculatepharmacokinetic parameters using PK Solutions Version 2.0. The method ofresiduals (i.e., curve stripping or feathering) was used to resolve theconcentration-time profile curve of M1 into a series of exponentialterms corresponding to the absorption, distribution, and eliminationphases occurring during the time course in the blood. These exponentialterms were then used to calculate the single-dose pharmacokineticparameters following well established formulae. The single-dosepharmacokinetic parameters were then used to calculate predictedsteady-state pharmacokinetic parameters, including Css_(min) andCss_(max), and their difference (ΔCss).

TABLE 10 Steady-State M1 PK dose >90% Single-Dose M1 PK Actual PredictedM1 tramadol released C_(max) T_(max) AUC_((0-t)) AUC_(∞) t_(1/2)Css_(max) Css_(min) ΔCss Form mg mg Hr ng/ml hr ng-hr/ml ng-hr/ml hrng/ml ng/ml ng/ml M₁ 20 — Instant 52.3 2.0 351 357 4.1 74 36 39 M₂ 40 —Instant 88.6 1.5 619 633 4.4 127 65 62 T₁ — 100 0.3 66.8 3.0 812 906 7.1163 125 38 T₂ — 100 0.3 54.2 3.0 587 749 12 120 73 46 SR103 40 — 3.873.1 3.0 504 519 4.2 108 17 91 SR104 40 — 6.9 53.8 5.0 538 566 6.3 94 6727 SR105 40 — 12.2 45.1 4.0 505 549 6.3 98 73 25 SR310 40 — 3.7 68.5 2.0532 554 5.4 105 55 50 SR308 40 — 8.0 71.6 1.5 593 705 10.7 133 76 57SR206 40 — 9.2 64.1 2.0 554 638 11.1 105 74 31 SR307 40 — 14 42.8 5.0470 544 9.2 92 64 28 SR203* 40 — 7.0 42.2 3.0 498 630 10.8 112 72 41SR306 40 — 12.0 ** ** ** ** ** ** ** ** SR102 20 7.4 28.8 3.6 219 2296.0 44 9 36 SR307 + T₃ 40  30 14 61.9 2.5 526 647 16 103 58 45 SR105 +T₃ 40  30 12 67.7 3.0 734 892 9.9 164 115 49 Abbreviations: M₁ =single-dose 20 mg M1 IR (solution A); M₂ = single-dose 40 mg M1 IR(solution A); T₁ = first single-dose 100 mg Tramadol IR (ULTRAM  ®); T₂= second single-dose 100 mg Tramadol IR (ULTRAM  ®) where T₁ and T₂ wereseparated by 25 months (January 2009 vs. February 2011); T₃ = 30 mgTramadol IR (ULTRAM  ®) given as a combination with an SR formulation;ΔCss = Css_(max) − Css_(min); *M1 free base, dose expressed as HCl saltequivalent; **Release delayed >12 hr and pharmacokinetic parameterscould not be computed.

The single-dose pharmacokinetic parameters and predicted steady-statepharmacokinetic parameters are summarized in Table 10. Thepharmacokinetic profiles for the SR+IR combination formulations,SR307+T₃ and SR105+T₃ are shown graphically in FIGS. 13A and 13B,respectively. The human data in this example demonstrated, (i) thatdifferent in vitro dissolution kinetics resulted in differentsingle-dose pharmacokinetic parameters, (ii) that different single-dosepharmacokinetic parameters result in different predicted values forCss_(min), Css_(max) and ΔCss, and (iii) that surprisingly, SR M1+IRtramadol combination formulations with certain dissolution kinetics andcertain M1 and tramadol doses substantially replicate the single-dose M1plasma profile obtained from a single dose of 100 mg tramadol. Thelatter is in sharp distinction to the very different single-dose M1plasma profile unexpectedly obtained when M1 was given as an IRformulation versus that from IR tramadol (see FIG. 1B and Example 6).

Example 11 In Vitro-In Vivo Correlation Model of Sustained ReleaseO-Desmethyltramadol

In vitro-in vivo correlation (IVIVC) is defined as the correlationbetween an in vitro drug dissolution profile and its in vivo drugabsorption profile. Using the single-dose human pharmacokinetic and invitro dissolution data for IR and SR dosage forms of M1 herein, an IVIVCmodel was developed that represented a point-to-point relationshipbetween in vitro dissolution rate and in vivo input rate of M1 for eachSR dosage form. The IVIVC model was developed in a two-stage processthat consisted of deconvolution and convolution. Deconvolution,convolution and other computations related to developing the IVIVC modelwere performed in IVIVC_0.1.5, a freely distributed software package forIVIVC modeling and validation.

Stage (1)—Deconvolution:

An oral solution of M1 HCl completely dissolved in water was employed toobtain the ‘reference plasma concentration profile’ for when there iszero delay in dissolution (i.e., no sustained release by definition). Inparticular, data from the oral dosing of 40 mg M1 dissolved in water(i.e., 40 ml of Solution A from Example 4) was collected in theprescribed comma delimited csv format and submitted to IVIVC_0.1.5 asthe reference plasma concentration profile. Pharmacokinetic parameters(k_(a), k_(el), V_(d)) were determined for the reference plasmaconcentration profile using the Nelder-Mead Simplex algorithm availablein IVIVC_0.1.5. Using the pharmacokinetic parameters of the referenceplasma concentration profile and the in vitro dissolution data for eachSR formulation, the fraction of M1 absorbed in vivo as a function oftime was predicted for each SR formulation by deconvolution using theWagner-Nelson method available in IVIVC_0.1.5.

Stage (2)—Convolution:

The predicted fraction of M1 absorbed in vivo as a function of time wasthen convolved to the predicted plasma concentrations by using theconvolution method available in IVIVC__(0.1.5).

TABLE 11 Mean Mean Time (hr) Prediction Prediction to >90% Error (%)Error (%) Formulation Released AUC C_(max) Monolithic CDT ® Series SR1033.8 5.4% 4.4% SR104 6.9 11.8% 10.1% SR105 12.2 7.6% 22.8% MonolithicHPMC Series SR203 7.0 9.1% 41.4% SR206 9.2 15.8% 34.2% Coated SeriesSR306 12.0 ** ** Monolithic KOLLIDON ® Series SR307 14 1.7% 9.0% SR3088.0 22.2% 31.9% SR310 3.7 10.8% 4.3% ** Release delayed >12 hr andpharmacokinetic parameters could not be computed.

The IVIVC model so developed was validated in IVIVC__(0.1.5) byevaluating the predictability of the correlation. The average‘prediction error’ in C_(max) and AUC for each SR formulation versus theactual data was calculated by IVIVC__(0.1.5)(Table 11).

The correlation coefficient between the predicted fraction absorbed invivo and the fraction released in vitro was computed (R²=0.80) for allSR formulations (FIG. 14). The actual versus IVIVC-model-predictedplasma concentration profiles are graphically depicted for each SRformulation series in FIGS. 15A, 15B, and 15C for monolithic CDT®tablets; FIGS. 16A and 16B for monolithic HPMC tablets; and FIGS. 17A,17B, and 17C for monolithic KOLLIDON® tablets.

Example 12 Human Steady-State Pharmacokinetics of Sustained ReleaseO-Desmethyltramadol

The same 88 kg healthy male subject in Example 6 was enrolled in anopen-label steady-state pharmacokinetic study. He received 10consecutive oral doses every 6 hours, each with water (sufficient toreach steady-state), of either SR100, SR101, SR102 or SR311. Eachten-dose sequence was separated by at least a 12 hour washout, althougha washout period was not strictly required in this study sincesteady-state is established by the 8^(th) dose, a time when there iseffectively no remnant of the previous dosing sequence. There were nofood or fasting restrictions.

For pharmacokinetic analysis, 23 venous blood samples (EDTA) were takenat about 0.0, 0.25, 0.50, 0.75, 1.0, 1.25, 1.5, 2, 3, 4, 5 and 6 hoursafter the 9^(th) and 0.25, 0.50, 0.75, 1.0, 1.25, 1.5, 2, 3, 4, 5 and 6hours after the 10^(th) doses (i.e., the 6 hour time point of the 9^(th)dose is equivalent to the 0.0 time point for the 10^(th) dose). Sampleswere centrifuged, and the plasma collected and stored frozen at −20° C.for analysis. There was no urine sampling in this study.0-desmethyltramadol in plasma samples was quantitated by an LC/MS assay(Warnex, Canada).

The steady-state pharmacokinetic parameters for the plasma M1concentrations are summarized in Table 12 for SR100, SR101, SR102 andSR311 (M1 IR HCl is also presented from Example 7 for comparison). Thesteady-state plasma M1 concentrations for the 9^(th) and 10^(th) dose ofSR102 are shown graphically in FIG. 18. For comparison, FIG. 18 alsoshows the steady-state plasma M1 profiles from Example 7 for the IRformulations of 20 mg M1 HCl, and 25, 50, 75 and 100 mg tramadol HCl(i.e., the commercially available immediate-release ULTRAM® tablets).

TABLE 12 >90% Dose Dose 9 Dose 9 Dose 10 Dose 10 Mean* Mean* Mean*released M1 HCl Css_(min) Css_(max) Css_(min) Css_(max) Css_(min)Css_(max) ΔCss T_(max)* Formula (hr) (mg) (ng/mL) (ng/mL) (ng/mL)(ng/mL) (ng/mL) (ng/mL) (ng/mL) (hr) Plasma M1 SR100 3.0 20 39 66 24 7531 71 40 2.5 SR101 5.1 20 43 69 27 62 35 65 30 1.6 SR102 7.4 20 31 46 2148 26 47 21 0.9 SR311 7.5 20 40 72 28 59 34 65 31 1.25 M1 IR^(†) instant20 34 94 34 108 34 101 67 1.25 *Mean of dose 9 and dose 10. ^(†)FromExample 7. ΔCss = Css_(max) − Css_(min).

Compared to the 20 mg IR HCl steady-state profile, SR100, SR101, SR102and SR311 all dampened the difference between mean Css_(max) andCss_(min) (i.e., ΔCss) for plasma M1 (Table 12). Surprisingly, thesteady-state plasma M1 profile for SR102 substantially replicated thesteady-state plasma M1 profile for ULTRAM® tablets at a dose of between25-50 mg (FIG. 18), as well as the ΔCss of 50 mg ULTRAM® (i.e., 21 vs.20 ng/mL, compare Table 3 to Table 12).

The human data in this example demonstrated that (i) SR M1 formulationswith different in vitro dissolution kinetics resulted in differentsteady-state pharmacokinetic parameters, and that (ii) surprisingly, SRM1 formulations with certain dissolution kinetics substantiallyreplicate the steady-state M1 plasma profile obtained from steady-statedosing of tramadol. In contrast to the inadequate (i.e., limited ornon-existent) M1 plasma profile seen in CYP2D6 poor metabolizersadministered tramadol who are resistant to its analgesic effects, SR M1formulations as provided herein provide an adequate therapeutic M1profile in all subjects irrespective of their CYP2D6 genotype.

Example 13 Human Steady-State Pharmacokinetics of Sustained ReleaseCombination Formulations

The same 88 kg healthy male subject in Example 6 was enrolled in anopen-label steady-state pharmacokinetic study. The study was performed,as in Example 12, with the subject administered (i) one SR102 tablet(i.e., 20 mg M1 in a sustained released formulation) simultaneously with15 mg IR tramadol HCl (i.e., ULTRAM®), or (ii) two SR102 tablets (i.e.,40 mg M1) simultaneously with 30 mg IR tramadol HCl.

TABLE 13 Dose 9 Dose 9 Dose 10 Dose 10 Mean* Mean* Mean* Css_(min)Css_(max) Css_(min) Css_(max) Css_(min) Css_(max) ΔCss Substance^(†)(ng/mL) (ng/mL) (ng/mL) (ng/mL) (ng/mL) (ng/mL) (ng/mL) Plasma M1  25 mgT 22 29 16 33 19 31 12  50 mg T 45 59 33 58 39 59 20  75 mg T 64 91 5381 58 86 28 100 mg T 88 114 58 113 73 114 41 SR102 + 15 mg T 57 97 64 7461 85 24 2x SR102 + 30 mg T 149 201 148 185 149 193 44 Plasma Parent  25mg T 53.6 101 50.5 137 52 119 67  50 mg T 136 269 141 294 139 282 143 75 mg T 198 368 193 438 196 403 208 100 mg T 316 560 310 627 313 594281 SR102 + 15 mg T 61 110 58 99 60 105 45 2x SR102 + 30 mg T 133 213145 238 139 226 87 ^(†)T = IR Tramadol HCl (ULTRAM ®). *Mean of dose 9and dose 10. ND = Not detected. ΔCss = Css_(max) − Css_(min).

The steady-state pharmacokinetic parameters for the plasma M1 and parentconcentrations are summarized in Table 13 (parameters for Tramadol IRHCl is also presented from Example 7 for comparison). The steady-stateplasma M1 concentrations for the 9^(th) and 10^(th) dose of thecombination formulations are shown graphically in FIG. 19. Thesteady-state plasma M1 profiles from Example 7 are shown for comparisonfor the IR formulations of 25, 50, 75 and 100 mg tramadol HCl (i.e.,commercial ULTRAM® tablets).

The steady-state plasma M1 profile for SR102 plus 15 mg IR tramadolsubstantially replicated the steady-state plasma M1 profile for ULTRAM®tablets at a dose of 75 mg (FIG. 19). Surprisingly, when IR tramadol wasadministered with SR102 as a combination, the average plasma M1 andtramadol levels were greater than predicted based on data for SR102(Example 12) and IR tramadol HCl (Example 7) administered separately.The actual versus predicted plasma profiles for M1 and tramadol areshown graphically in FIGS. 20A and 20B, respectively.

The human data in this example demonstrated that (i) SR M1 and IRtramadol combination formulations substantially replicate thesteady-state M1 plasma profile obtained from steady-state dosing oftramadol, and (ii) SR M1 plus IR tramadol combination formulations havemean plasma M1 and plasma tramadol levels higher than predicted based onlevels for each administered individually.

Example 14 Sustained Release Combination Tablets

Two preferred sustained-release (SR) combination tablets are shown inTable 14.

TABLE 14 Monolithic SR Combination Bilayer SR + IR Combination TabletSR106 Tablet SR107 SR Core SR Layer IR Layer Raw Material PurposeManufacturer (mg/tablet) (mg/tablet) (mg/tablet) M1 HCl API 1 In-House20.0 20.0 — Tramadol HCl API 2 In-House 15.0 — 15.0 HPMC K4M PolymerColorcon 100.0 50.0 — Na Bicarbonate Electrolyte Natrium 50.0 25.0 —AVICEL MCC PH 102 Flow Agent FMC 105.0 50.0 83.0 Colloidal SilicaGlidant Cabot — — 1.0 Mg Stearate Lubricant Mallinckrodt 3.0 1.5 1.0Total mg/tablet 293.0 146.5 100.0 HPMC = hydroxypropylmethyl cellulose;MCC = microcrystalline cellulose.

SR106 is manufactured as described in Example 8 for SR105. SR107 isprepared by separately homogeneously mixing the raw materials of the SRLayer and IR Layer. The two mixtures are then compressed in a tabletpress (Korsch EKO) to provide a bilayer tablet by introducing 146.5 mgof the first SR Layer mixture into the die and precompressing by handand, after addition of 100 mg of the second IR Layer mixture, finallyfully compressing the tablet.

Example 15 Human Steady-State Pharmacokinetics of Sustained ReleaseCombination Tablets

Healthy subjects will be enrolled in an open-label steady-statepharmacokinetic study to receive 10 consecutive oral doses every 6hours, each with water (sufficient to reach steady-state) of: 1 tabletof SR106, 2 tablets of SR106, 1 tablet of SR107, 2 tablets of SR107, 1tablet tramadol and/or 2 tablets tramadol (each tramadol tablet is anULTRAM® 50 mg tablet). Each ten-dose sequence will be separated by atleast a 12 hour washout, although a washout period is not strictlyrequired. There will be no food or fasting restrictions. Pharmacokineticanalysis will be as in Example 12. Subjects taking 1-2 tablets of SR106or SR107 will have an M1 steady-state profile substantially the sameirrespective of their CYP2D6 genotype, and within the range of the M1profile in normal metabolizers taking 1-2 tablets of tramadol. Allsubjects will be exposed to the parent molecule (i.e., racemic tramadolitself) irrespective of subject CYP2D6 genotype. Thus, irrespective ofCYP2D6 genotype, SR106 and SR107 will provide both the M1 metabolite andthe parent drug and restore the entire spectrum of opioid andmonoaminergic activity seen in normal subjects after dosing withconventional tramadol.

Example 16 Combination Formulations

M1 and tramadol combinations that provide suitable therapeuticsteady-state plasma M1 and tramadol profiles are shown in Table 15.

TABLE 15 X mg M1:Y mg tramadol 5:5   5:7.5  5:10   5:12.5  5:15  5:20 5:25  5:30  5:35  5:40 7.5:5   7.5:7.5 7.5:10   7.5:12.5 7.5:15 7.5:20  7.5:25  7.5:30  7.5:35  7.5:40  10:5   10:7.5 10:10   10:12.510:15 10:20 10:25 10:30 10:35 10:40 12.5:5   12.5:7.5  12.5:10  12.5:12.5 12.5:15   12.5:20   12.5:25   12.5:30   12.5:35   12.5:40  15:5   15:7.5 15:10   15:12.5 15:15 15:20 15:25 15:30 15:35 15:40 20:5  20:7.5 20:10   20:12.5 20:15 20:20 20:25 20:30 20:35 20:40 25:5  25:7.5 25:10   25:12.5 25:15 25:20 25:25 25:30 25:35 25:40 30:5  30:7.5 30:10   30:12.5 30:15 30:20 30:25 30:30 30:35 30:40 35:5  35:7.5 35:10   35:12.5 35:15 35:20 35:25 35:30 35:35 35:40 40:5  40:7.5 40:10   40:12.5 40:15 40:20 40:25 40:30 40:35 40:40Bolded combinations indicate preferred combinations. The M1 ispreferably a SR formulation, and the tramadol is preferably an IRformulation. The M1 formulation is more preferably SR102.

I claim:
 1. A sustained release dosage form, comprising atherapeutically effective amount of O-desmethyltramadol, or apharmaceutically acceptable salt thereof, and pharmaceutical excipients;wherein the sustained release dosage form comprises a matrix, reservoir,coated-bead or multi-particulate; wherein the sustained release oraldosage form has a dissolution rate consisting of between 15 and 74%O-desmethyltramadol released at 1 hour, between 28 and 91%O-desmethyltramadol released at 2 hours, between 38 and 101%O-desmethyltramadol released at 3 hours, between 47 and 105%O-desmethyltramadol released at 4 hours, between 59 and 105%O-desmethyltramadol released at 6 hours, between 68 and 105%O-desmethyltramadol released at 8 hours, between 75 and 105%O-desmethyltramadol released at 10 hours, between 79 and 105%O-desmethyltramadol released at 12 hours, 100% O-desmethyltramadolreleased at 24 hours, by weight; and wherein upon administration to ahuman subject delivers O-desmethyltramadol with a half-life of 5.4 to11.1 hours.
 2. The sustained release dosage form of claim 1, comprisinga parenteral sustained-release dosage form.
 3. The sustained releasedosage form of claim 2, comprising an intravenous, subcutaneous, orintramuscular sustained-release dosage form.
 4. The sustained releasedosage form of claim 1, comprising an oral sustained-release dosageform.
 5. The sustained release dosage form of claim 4, comprising atablet or capsule.
 6. The sustained release dosage form of claim 1,wherein the O-desmethyltramadol is 1-40 wt %.
 7. The sustained releasedosage form of claim 1, wherein the O-desmethyltramadol is the soleactive pharmaceutical ingredient.
 8. The sustained release dosage formof claim 1, further comprising a drug selected from the group consistingof tramadol, acetaminophen, aspirin, ibuprofen, diclofenac, naproxen,indomethacin, fenoprofen, oxycodone, hydromorphone, codeine, hydrocodoneand topiramate.
 9. The sustained release dosage form of claim 1, whereinthe O-desmethyltramadol is (1S, 2S)—O-desmethyltramadol, a combinationof both (1R, 2R)—O-desmethyltramadol and (1S, 2S)—O-desmethyltramadol,or a pharmaceutically acceptable salt thereof.
 10. The sustained releasedosage form of claim 1, wherein the therapeutically effective amount ofO-desmethyltramadol is from 5 mg to 100 mg.
 11. The sustained releasedosage form of claim 1, wherein the pharmaceutical excipients comprise apolymer or lipid.
 12. The sustained release dosage form of claim 1,wherein the pharmaceutical excipients are selected from the groupconsisting of polyvinylpyrrolidone, hydroxypropylmethyl cellulose,hydroxypropylcellulose, ethylcellulose, polyalkylene oxide, polyvinylacetate, microcrystalline cellulose, cellulose ethers, xanthan gum,alginate, a buffer, talc, colloidal silica, magnesium stearate,polysaccharide, polyalkylene glycol, protein-derived materials, fattyacids, fatty alcohols, glycerides, glyceryl esters of fatty acids,mineral oils, vegetable oils and waxes.
 13. The sustained release dosageform of claim 1, wherein O-desmethyltramadol is a hydrochloric acidsalt.
 14. The sustained release dosage form of claim 1, wherein thesustained release oral dosage form has a dissolution rate selected fromthe group consisting of, between 21 and 72% O-desmethyltramadol releasedat 1 hour; between 34 and 89% O-desmethyltramadol released at 2 hours;between 44 and 99% O-desmethyltramadol released at 3 hours; between 52and 105% O-desmethyltramadol released at 4 hours; between 65 and 105%O-desmethyltramadol released at 6 hours; between 70 and 105%O-desmethyltramadol released at 8 hours; between 81 and 105%O-desmethyltramadol released at 10 hours; between 86 and 105%O-desmethyltramadol released at 12 hours; and about 100%O-desmethyltramadol released at 24 hours, by weight.
 15. The sustainedrelease dosage form of claim 1, wherein the sustained release oraldosage form has a dissolution rate selected from the group consistingof, between 25 and 54% O-desmethyltramadol released at 1 hour; between40 and 69% O-desmethyltramadol released at 2 hours; between 52 and 82%O-desmethyltramadol released at 3 hours; between 61 and 92%O-desmethyltramadol released at 4 hours; between 78 and 101%O-desmethyltramadol released at 6 hours; between 83 and 105%O-desmethyltramadol released at 8 hours; between 89 and 105%O-desmethyltramadol released at 10 hours; between 91 and 105%O-desmethyltramadol released at 12 hours; and about 100%O-desmethyltramadol released at 24 hours, by weight.
 16. The sustainedrelease dosage form of claim 1, wherein the sustained release oraldosage form has a dissolution rate selected from the group consistingof, between 25 and 35% O-desmethyltramadol released at 1 hour; between40 and 50% O-desmethyltramadol released at 2 hours; between 52 and 62%O-desmethyltramadol released at 3 hours; between 61 and 71%O-desmethyltramadol released at 4 hours; between 78 and 88%O-desmethyltramadol released at 6 hours; between 83 and 93%O-desmethyltramadol released at 8 hours; between 89 and 99%O-desmethyltramadol released at 10 hours; between 91 and 105%O-desmethyltramadol released at 12 hours; and about 100%O-desmethyltramadol released at 24 hours, by weight.
 17. The sustainedrelease dosage form of claim 1, wherein the sustained release oraldosage form upon administration to a subject produces a plasma profileof O-desmethyltramadol that substantially replicates the plasma profileof O-desmethyltramadol following administration of tramadol.
 18. Thesustained release dosage form of claim 1, wherein the compositioncomprises two or more phases, wherein a first phase comprisesO-desmethyltramadol or a pharmaceutically acceptable salt thereof, and asecond phase is racemic tramadol or a pharmaceutically acceptable saltthereof.
 19. The sustained release dosage form of claim 18, wherein thefirst phase comprises a major part of O-desmethyltramadol or apharmaceutically acceptable salt thereof and the second phase comprisesa major part of racemic tramadol; or wherein the first and second phasesare in the form of a plurality of layers, and wherein at least one layercontains O-desmethyltramadol or a pharmaceutically acceptable saltthereof and at least another layer contains racemic tramadol.
 20. Thesustained release dosage form of claim 1, further comprising a coating.21. The sustained release dosage form of claim 20, wherein the coatingcomprises polymethacrylate, alkyl cellulose, water-soluble cellulose,polysorbate, polyvinylpyrrolidone, polyvinylalcohol, polyethylene glycolor a derivative thereof, triethyl citrate, or dibutyl sebacate.
 22. Thesustained release dosage form of claim 1, wherein the dissolution rateis measured using a USP Method is a USP Apparatus I Basket Method at 75rpm in 900 mL 0.05 M phosphate buffer at pH 7.2 at 37° C.
 23. Thesustained release dosage form of claim 1, wherein the therapeuticallyeffective amount of O-desmethyltramadol is 5, 10, 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100 mg.
 24. Thesustained release dosage form of claim 1, wherein the therapeuticallyeffective amount of O-desmethyltramadol is from 5 to 25 mg, 5 mg to 50mg, 5 mg to 100 mg, or 5 mg to 200 mg.
 25. The sustained release dosageform of claim 1, wherein the sustained release dosage form comprises amatrix.
 26. The sustained release dosage form of claim 1, wherein thesustained release dosage form comprises a coated bead.
 27. The sustainedrelease dosage form of claim 1, wherein the sustained release dosageform comprises a reservoir.
 28. The sustained release dosage form ofclaim 27, wherein the reservoir comprises a glyceride.
 29. The sustainedrelease dosage form of claim 28, comprising an intravenous dosage form.30. A sustained release dosage form, comprising a therapeuticallyeffective amount of O-desmethyltramadol, or a pharmaceuticallyacceptable salt thereof, and pharmaceutical excipients; wherein thesustained release dosage form comprises a matrix, reservoir, coated-beador multi-particulate; wherein the sustained release oral dosage form hasa dissolution rate consisting of between 15 and 74% O-desmethyltramadolreleased at 1 hour, between 28 and 91% O-desmethyltramadol released at 2hours, between 38 and 101% O-desmethyltramadol released at 3 hours,between 47 and 105% O-desmethyltramadol released at 4 hours, between 59and 105% O-desmethyltramadol released at 6 hours, between 68 and 105%O-desmethyltramadol released at 8 hours, between 75 and 105%O-desmethyltramadol released at 10 hours, between 79 and 105%O-desmethyltramadol released at 12 hours, 100% O-desmethyltramadolreleased at 24 hours, by weight; and wherein upon administration to ahuman subject delivers O-desmethyltramadol with a difference betweenminimum and maximum plasma concentration of O-desmethyltramadol atsteady state is not more than 40 ng/mL.
 31. The sustained release dosageform of claim 30, wherein the difference between minimum and maximumplasma concentration of O-desmethyltramadol at steady state is not morethan 30 ng/mL.
 32. A sustained release dosage form, comprising atherapeutically effective amount of O-desmethyltramadol, or apharmaceutically acceptable salt thereof, and pharmaceutical excipients;wherein the sustained release dosage form comprises a matrix, reservoir,coated-bead or multi-particulate; and wherein upon administration to ahuman subject delivers O-desmethyltramadol with a half-life of 5.4 to11.1 hours.